Kim, Khloé and Kourtney Kardashian
Karl Milan/Splash News Online
05/25/2011 at 07:15 PM EDT
was taken by surprise when Kris Humphries popped the question
, but the reality star's mom and stepdad knew it was coming.
Kris and Bruce Jenner found out "a few days" before it happened, Kim's mom revealed Wednesday during a press day for the family's show Keeping Up with the Kardashians
"He came to Bruce and myself and asked us for Kim's hand in marriage," says Kris Jenner, "and it was really just so cute the way that he wanted to surprise her."
Humphries, 26, waited in Kim's bedroom on bended knee with four words written in red rose petals: "WILL YOU MARRY ME?"
Mom Kris decided to host a family dinner in honor of the occasion – without revealing the reason to the rest of the family.
"[Kim and Kris] were going to come over to my house, join the party, and then tell the rest of the family," says Kris Jenner.
But sisters Khloé and Kourteny Kardashian were totally in the dark about the news. "We had no idea! We were both surprised at the dinner when Kim came out with her big rock
and she started waving it in the air," says Kourtney.
As for moving ahead with wedding planning, Khloé says that Kim will be totally in control of every element: "Kim, trust me, will never let anyone else touch her wedding but herself."
But the sisters do plan to have a role in the nuptials. "I would assume that we would both be maids of honor," says Khloé.
Quips Kourtney: "We're assuming, because otherwise there would be a war."