Kate Middleton sips Guinness in green as she and Prince William attend St Patrick’s Day parade

KATE Middleton today primly sipped a small glass of Guinness as she joined St Patrick's Day celebrations.

The Duchess of Cambridge and husband Prince William beamed as they knocked back the traditional Irish stout with officers after attending the parade of the Irish Guards this morning at the Cavalry Barracks.

The 37-year-old duchess donned a dark green Alexander McQueen coat and hat from Lock and Co along with Gianvito Rossi pumps for the day out to celebrate St Paddy's Day.

And she and husband Prince William made sure to join the celebrations as they sipped a glass each of the black stuff.

But while the Duke of Cambridge had his drink in a traditional pint glass, Kate seemed to hold back with a smaller cup during the visit to the 1st Battalion at their base in Hounslow, west London.

And the mum-of-three seemed to be delighted with the day of celebrations - getting the chance to again meet Domhnallan, the Irish wolfhound and mascot again.

Domhnall, which is Gaelic for "world leader", led 350 soldiers as they marched on the Parade Square at Cavalry Barracks on Sunday morning.

The Duke and Duchess of Cambridge beamed during the ceremony as Kate presented shamrocks to officers and warrant officers.

During today's service, the couple led a minute's silence to pay respects to the New Zealand terror attack victims.

Since 1901, when the regiment was first founded by order of Queen Victoria, the regiment's parade has traditionally been presided over by a woman.

At past parades the Duke, who is Colonel of the Irish Guards, has sipped on a pint of Guinness in a nod to the tradition of the day.

Last year Kate, who was heavily pregnant with the couple's third child, opted for a sparkling water instead.

Three years of ceremonial duties for the Irish Guards came to an end in January.

The main focus of the past 12 months was on exercise Askari Storm, a battlegroup exercise in Kenya.

It currently has troops deployed in Uganda, Jordan and Kenya, and training will ramp up in September ahead of missions to South Sudan and Iraq.

Alongside its role serving in British conflicts overseas, the Irish Guards also serve in ceremonial and public duties at Buckingham Palace, Windsor Castle, St James's Palace and the Tower of London.