Khloe and Kourtney Kardashian were "totally surprised" at sister Kim's engagement.

The siblings insist they were stunned to learn NBA star Kris Humphries popped the question to the socialite because they had no idea a family get together was actually a Celebration for the couple.

Khloe said: "None of [the rest of] us knew. We were all sitting there like, 'Kim is so late for dinner and we're starving.' And we're like, 'Where the hell is Kim?'

"Then she walked in, and we were like, 'Oh my God!' But we just thought we were going to a family dinner."

Despite their surprise, Khloe and Kourtney are thrilled for Kim - who has been dating the sportsman for six months - because they know how happy Kris makes her.

Kourtney told "She's always smiling. There is a different happiness about her. Her priorities are more right with him. He grounds her in a way."

Kim, 30, previously admitted she was in "shock" when Kris got down on one knee with a 20.5 carat Lorraine Schwartz diamond ring - which the basketball star reportedly splashed out $2 million on - in her Beverley Hills home.

She said: "I didn't expect this at all. I was in such shock. I never thought it would happen at home, and I never thought now."