Kim Kardashian's brother has doubts whether she will actually marry Kris Humphries.

The reality TV star and the basketball player announced their engagement earlier this week and while Kim has started planning her nuptials, Rob Kardashian isn't convinced the wedding will happen.

He told radio station Kidd Kraddick and Hyla on the Hollywood 5: "I just don't feel confident because Kim has always been so like, you know, she's, how old?

"She's just been through a lot of relationships and she always gets hurt or never finds the right dude, but Kris is a really good dude."

However, Rob believes if 30-year-old Kim is going to make it with anyone, it will be Kris.

He said: "They've had their own personal, private relationship a long time now and I feel like they are a really good match for each other."

He also revealed how the family thought Kim and Kris - who have been dating for six months -- were joking when they first told everyone about the engagement.

He said: "We were having a family dinner and we didn't know what it was for, we just thought everyone was in town, we were at my mom's. She had a ring on and we didn't know what it was for, and we didn't believe her and we thought it was a joke, no one really, like, did anything, and it was like, oh wait, then it got crazy and there were ponies, it was really bizarre!

"Congrats to her, it was pretty shocking in my mind."