KUWTK fans gush over Rob Kardashian’s ‘sexy’ slim figure in rare show cameo as he ‘regained confidence’ with weight loss

The father of one "cut out the junk food" and has been "sticking to a high-protein diet."

"The Kardashians are proud of Rob for losing so much weight. More than anything, they’re relieved that he’s taking better care of himself," the insider added.

He also is has been working out with sister Khloe Kardashian at her home gym, with the pair joined by her beau Tristan Thompson, "doing cardio, running, pushups and deadlifting."

In July, Khloe, who is super close to Rob, spoke out about how proud she was of him for focusing on his health.

"He’s so handsome, he’s such a good person and I just love him,” the mom of one said.

"And I love that he’s getting a positive response because it’s just gassing him up more. It makes him feel really good and confident. That’s all I want for my brother."

Fans are promised to see a lot of changes in 's life as season 20 airs after his major weight loss and amid his decision to start "casually dating."

Though the star now keeps his personal life private, he has battled baby mama Blac Chyna in a nasty custody battle for years.

After briefly dating, the former couple welcomed four-year-old daughter, Dream, on November 10, 2016.

Shortly after the birth of their daughter, the pair split and have challenged each other in court in the years since.