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"I've never heard such crap in my life," Jenner, 56, said on Good Morning America on Thursday. "I was there. I gave birth. I know who the dad was."
The allegations that Khloe is not Robert's biological child were put forth by Jan Ashley and Ellen Kardashian, the two women Robert married after his 1990 divorce from Kris, in interviews with Star magazine.
"Khloe is not his kid -- he told me that after we got married," Ashley told the tabloid. "He just kind of looked at me and said (it) like it was a matter of fact. He said, 'Well, you know that Khloe's not really a Kardashian, don't you? And I said... 'OK,' and that was it."
"Robert did question the fact that Khloe was his," Ellen Kardashian agreed. "Any normal man would if they knew their wife had cheated on him... (But) he never would have considered a DNA test. He loved her very much."
Jenner, for her part, has admitted to cheating on Kardashian during their marriage -- but based on her statement on GMA, she believes Robert to be Khloe's dad.
So too does Khloe, who took to Twitter Wednesday to lash out at Robert's former wives.
"The audacity you have to mention my father's name like this! Should be ashamed of urself!" Khloe, 27, tweeted. "I let a lot of things slide but this one is really low… YOU ARE DISGUSTING! (yes you know who YOU are)."
But Jenner has just decided to laugh off the whole incident. "It's all good," she says regarding the rumors. "It's the family joke. People, get a life."
As for why Robert's other wives made the claims, Kris had this to say: "Maybe it makes somebody relevant for the day, and tomorrow it'll be something else." It always is with those kooky Kardashians!