Rob Kardashian knows he is "fat."

The 'Keeping Up with the Kardashians' star - who was pictured at LAX airport on Sunday, the first time he has been seen in public for several weeks - laughed off reports he has been to rehab or "fat camp" to address his weight problems, and insists he will do something about his size when he feels ready to.

He tweeted: "so i found out i was trending for being fat... thank you all it really made my day :)

"and to the blogs saying i went to fat camp or rehab LOL then why am i still fat u fools?? y'all must have run out of real news.

"first, i don't believe in rehab or therapy or anything of that sort and second I'm a grown man and will work on myself when i choose

"I'm aware that I'm fat that def aint a surprise to me lol and my only therapy will be in the gym anyways had to say somethingggggggggg (sic)"

Rob was recently warned by doctors he risked an early death if he didn't tackle his weight problem after undergoing medical testing.

In scenes which aired on "Keeping Up with the Kardashians" recently, the doctor advised Rob was at risk of developing diabetes and eventual organ failure, prompting his mother Kris Jenner to give her 26-year-old son a stark warning.

She told him "Your liver is shutting down.

"This is life-threatening at this point. You can only sustain this level of being unhealthy for so long."

The shocking news came weeks after the sock designer admitted to his older sister Khloe Kardashian that his weight gain has made him depressed.

He recently said: "I've never felt so down depressed in my life. I'm trying to be in the fashion industry and I'm not going to be taken seriously when I'm fifty pounds overweight. It's embarrassing to the family."