PRINCE William was supported by Princess Diana's sister today as he said we "live in a time of uncertainty" at the Sovereign’s Parade.
The Prince of Wales, 42, wore his beard with his Wing Commander uniform as he joined the parade at the Royal Air Force College in Cranwell, Lincolnshire.
Speaking at the event, William told new RAF officers the country will be relying on them to deal with "future threats" during the present "time of change and uncertainty".
And he was joined at the bash by Lady Sarah McCorquodale, 69, who is his aunt - and Princess Diana's sister.
It is understood Lady Sarah heard her nephew was at the event and turned up to show "support".
She lives 15 miles from RAF Cranwell, in Grantham, and she served a one-year term as High Sheriff of Lincolnshire in 2009.
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The prince spoke during the graduation ceremony of more than 50 officers who have completed their training at the Royal Air Force College Cranwell.
He knows RAF Cranwell in Lincolnshire well, as he trained at the air force base, flying solo for the first time and later received his wings from his father during a ceremony at Cranwell in 2008.
He remained in the RAF for much of his active military career going on to fly as a helicopter pilot in the RAF Search and Rescue Force before becoming an air ambulance helicopter pilot.
In his speech William said: "We live in a time of change and uncertainty, and you, as the future of the Royal Air Force, are the ones who will ensure that we are able to adapt and face future threats."
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During the graduation parade William acknowledged the royal salute of the 54 new officers on the parade ground, who as cadets spent up to 24 weeks being taught about leadership, underwent strenuous military exercises and other training.
The prince said: "Whilst I didn't graduate on this exact parade ground, I did graduate from flying training here so I know something about the celebrations that will come later, so I promise, I'll only take a few minutes of your time!
"I do want to take this moment though, to highlight not only the importance of your achievements to date, but also that of the roles you will play in supporting the futures of your countries' air forces.
"I say 'your countries', as I know that in addition to our newest Royal Air Force officers on parade today, there are also officers from Jordan, Kenya, Pakistan and Uganda.
"Multi-national relationships are key to international defence, security, and peace.
"The relationships you have formed through training, will be key in allowing you to achieve success in future roles, and enhancing the security of all our nations."
It comes after he told royal fans on Wednesday during a visit to Llanelli, Carmarthenshire, that wife Princess Kate "still has a long way to go" despite her chemo treatment now complete.
The royal couple and their three children appeared in a video on Monday, shot during a family holiday to Norfolk, in which she said she is cancer free.
Today's parade included graduates from the Commissioned Warrant Officers Course and Modular Initial Officer Training Course.
KATE'S CANCER UPDATE: THE TIMELINE OF HER 'INCREDIBLY TOUGH' NINE MONTHS
January 16
Kate is secretly admitted to The London Clinic and undergoes abdominal surgery.
She attends the clinic rather than King Edward VII's Hospital, which is usually the go-to establishment for royal family medical matters.
January 17
2pm - Kensington Palace announces the princess's operation and says she will remain in the private hospital for 10-14 days.
She is not expected to return to duties until after Easter, taking up to three months to recover.
The Prince of Wales steps back from his official duties temporarily to care for his wife and children.
The exact nature of Kate's condition is kept private, but it is not cancerous and Kensington Palace says the planned procedure was successful.
A source later says the princess is "doing well".
January 18
The Prince of Wales spends time at his wife's bedside, driving himself away from the back entrance during the low-key, private visit.
A serious-looking William was seen leaving the The London Clinic at about 12.35pm.
January 23
Kate's hospital stay passes the one-week mark.
January 26
The King visits the Princess of Wales after he is admitted to The London Clinic for treatment for an enlarged prostate.
January 29
Kate leaves the clinic to continue her recovery at home.
February 5
Kensington Palace confirms the Prince of Wales is returning to official duties that week, beginning with an investiture.
Buckingham Palace announces the King has a form of cancer, but not prostate cancer, and has started treatment as an outpatient.
He will not carry out public-facing duties, but will carry on with behind-the-scenes state business and official papers, the Palace says.
February 7
William thanks the public for their "kind messages of support" after the King announced his cancer diagnosis, while also recognising those who wished Kate well as she recovered from planned abdominal surgery.
March 4
The princess is photographed for the first time since undergoing abdominal surgery.
Kate is pictured in paparazzi shots near Windsor Castle wearing dark sunglasses in the passenger seat of a car, which was being driven by her mother, Carole Middleton.
March 5
The Army removes a claim on its website that the princess was reviewing Trooping the Colour in June.
Tickets were being sold on the official website for the June 8 military event, advertising an appearance by Kate.
March 10
Questions are raised that the first picture of the princess to be released after her abdominal surgery may have been manipulated before it was posted on social media by Kensington Palace.
The photo of Kate and her children, said by the palace to have been taken by William in Windsor earlier in the week, was celebrating Mother's Day.
In the post, Kate said: "Thank you for your kind wishes and continued support over the last two months.
"Wishing everyone a Happy Mother's Day. C."
The picture shows Kate sitting in a chair with her arms around Princess Charlotte and Prince Louis, who are on either side of her, with Prince George standing behind, as all four smile at the camera.
The photograph, shared with the media, is withdrawn by international picture agencies later the same day because of concerns that the image had been manipulated.
March 11
Kate publicly takes the blame for the manipulated photograph and issues a personal apology for the "confusion".
Kate says: "Like many amateur photographers, I do occasionally experiment with editing.
"I wanted to express my apologies for any confusion the family photograph we shared yesterday caused.
"I hope everyone celebrating had a very happy Mother's Day. C."
March 16
The princess is filmed smiling with her husband during a visit to a farm shop in Windsor.
March 19
An investigation is launched at The London Clinic over claims staff tried to access the princess' private medical records.
At least one member of staff allegedly tried to access Kate's notes while she was a patient at the hospital in January.
The UK privacy and data protection watchdog says it has received a breach report.
March 22
Kate announces she is undergoing chemotherapy for cancer in an emotional video message.
She describes the "huge shock" after tests identified cancer following her abdominal surgery and the "incredibly tough couple of months" her family has experienced.
"It has taken us time to explain everything to George, Charlotte and Louis in a way that is appropriate for them, and to reassure them that I am going to be OK," she adds
April 18
William, who had spent the previous three and a half weeks with Kate and their children during the Easter holidays, returns to public work.
He visits Surplus to Supper, a surplus food redistribution charity, in Sunbury-on-Thames, and then a youth centre in west London.
May 10
William gives a positive update about his wife's treatment during a visit to the Isles of Scilly, saying "she's doing well".
June 5
The prince chats to a veteran at a D-Day commemorative event in Portsmouth, and appears to suggest Kate is getting better, adding: "She'd love to be here today."
June 8
The Princess of Wales writes a letter to the Irish Guards to apologise for not being able to take the salute, and wishes them luck for The Colonel's Review in London.
June 14
Kate issues a written message saying she is "making good progress" and has "good days and bad days", adding: "I am not out of the woods yet."
She confirms she will attend Trooping the Colour and that she "hopes to join a few public engagements over the summer" as she continues treatment "for a few more months".
A new photograph of the royal, taken earlier the same week in the grounds of the Windsor Castle estate, shows Kate stood in a tranquil setting against a weeping willow tree near a body of water.
June 15
The princess looks relaxed during her first day in the spotlight following her cancer diagnosis at the traditional Trooping ceremony.
She takes part in the carriage procession and joins the royal family including George, Charlotte and Louis on the Palace balcony.
July 14
Kate presents the Wimbledon men's final trophy to Carlos Alcaraz, in her second public engagement since her diagnosis.
The princess, patron of the All England Lawn Tennis and Croquet Club, is accompanied by her daughter Charlotte and chats to ball boys and girls and enters Centre Court to loud applause.
August 11
William, sporting a beard, and Kate appear in a video message congratulating Team GB after the Paris Olympics, with a compilation of messages from celebrities including Snoop Dogg and David Beckham.
August 25
Kate joins William, and the King and Queen at Crathie Church, near Balmoral Castle, in Scotland during a summer break in the Scottish Highlands.
September 6
The princess says she is "looking forward to working" with the UK's new chief scout, Dwayne Fields.
A personal welcome message from Kate, who is joint president of the Scout Association, was posted on the Waleses' official social media account.
September 8
Reports say Kate is hoping to join the royal family at the Cenotaph on Remembrance Sunday and host her Christmas carol concert.
September 9
The Princess of Wales says she has finished chemotherapy and is "looking forward to being back at work and undertaking a few more public engagements in the coming months" but adds her focus is on "doing what I can to stay cancer free".
She shares a video montage of precious family time spent with William and her children over the summer.
In a personal message, Kate says "although I have finished chemotherapy, my path to healing and full recovery is long".
She adds: "To all those who are continuing their own cancer journey - I remain with you, side by side, hand in hand."
In total, 48 Royal Air Force Cadets are passing out, alongside four International Officer Cadets from Jordan, Kenya, Pakistan and Uganda.
The cadets have undergone up to 24 weeks of intensive training, which prepares them with the skills and knowledge required to set the foundations for a successful career in the RAF.
William has been overseeing a Royal Salute and watching a fly past over the college, along with inspecting the front rank of the Guard during the parade, and presenting four awards.
Following his short speech congratulating the graduates, he is joining the graduating officers, their friends and families in the College Dining Room to hear about their experiences of the training programme and their hopes for their future careers.
William had thanked fans for their support on Wednesday amid news of Kate's chemotherapy coming to an end.
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He told Pauline Thomas, 74: “It’s good news but there is still a long way to go.”
The Prince and Princess of Wales posted a message of thanks on social media, in both the English and Welsh languages.
Princess Kate's statement in full
PRINCESS Kate revealed on Monday that she is now cancer free after completing chemotherapy.
In a statement she said: "As the summer comes to an end, I cannot tell you what a relief it is to have finally completed my chemotherapy treatment.
"The last nine months have been incredibly tough for us as a family. Life as you know it can change in an instant and we have had to find a way to navigate the stormy waters and road unknown.
"The cancer journey is complex, scary and unpredictable for everyone, especially those closest to you.
"With humility, it also brings you face to face with your own vulnerabilities in a way you have never considered before, and with that, a new perspective on everything.
"This time has above all reminded William and me to reflect and be grateful for the simple yet important things in life, which so many of us often take for granted. Of simply loving and being loved.
"Doing what I can to stay cancer free is now my focus. Although I have finished chemotherapy, my path to healing and full recovery is long and I must continue to take each day as it comes.
"I am however looking forward to being back at work and undertaking a few more public engagements in the coming months when I can.
"Despite all that has gone before, I enter this new phase of recovery with a renewed sense of hope and appreciation of life.
"William and I are so grateful for the support we have received and have drawn great strength from all those who are helping us at this time. Everyone’s kindness, empathy and compassion has been truly humbling.
"To all those who are continuing their own cancer journey – I remain with you, side by side, hand in hand. Out of darkness, can come light, so let that light shine bright."