Kris Jenner says she cries herself to sleep over her son

TV personality Kris Jenner poses for a portrait in New York on Monday July 8, 2013. (Dan Hallman / Invision)

Kris Jenner cries herself to sleep.

The 58-year-old matriarch admits she falls asleep weeping over her son Rob Kardashian, 27, after he plunged into depression following his weight gain.

Speaking to her daughter Kim Kardashian, 33, in a preview of Sunday's episode of 'Keeping Up with the Kardashians', Jenner said: "I want to fix Rob and sometimes you just can't. I have not not cried myself to sleep in so long that I don't even know what that's like. It's the worst feeling in the world when one of your kids isn't in a good place."

However, Kim Kardashian, who has 13-month-old daughter North with her husband Kanye West, insists she doesn't feel sorry for her younger brother and thinks he needs to stop moping and do something to improve the situation.

"We've all been here to offer him help and he won't take it, so I don't have sympathy," she said in the last episode of the reality TV show after Rob failed to attend a family vacation to Thailand.

She then turned to the camera and explained: "I think I'm just more of the tough love kind of person. My personality is like, 'All right, you complain, you don't like it, get up and do something about it.'"

Rob Kardashian has reportedly been distant from his relatives since he refused to attend his sister Kim's wedding in May following a huge family bust-up.