A report in Star magazine suggests Kim Kardashian's sister Khloe is not a true Kardashian because late lawyer Robert Kardashian is not her biological father.

The story is backed by the attorney's widow Ellen, who suggests that Khloe is her mother Kris Jenner's lovechild and therefore doesn't share the same father as her siblings. Ellen Kardashian also claims her late husband told her before he died in 2003 that the youngest Kardashian sister was not his daughter.

The story prompted a furious response from Khloe herself, who blasted the woman via her Twitter page on Wednesday to address the report.

She rages, "The audacity you have to mention my father's name like this! (You) should be ashamed of urself (sic)!

"I let a lot of things slide but this one is really low... YOU ARE DISGUSTING! (yes you know who you are)."

Robert Kardashian's widow claims the attorney wasn't sleeping with his then-wife Kris when Khloe was conceived and Jenner admits she did have an affair with a younger man - but after her daughter was born.

Revealing the extra-marital affair while promoting her memoirs on TV show Access Hollywood last year, Jenner said, "I was young and dumb and I had been with Robert since I was a teenager... I think that I got caught up in something that I regret."

And Khloe herself has questioned her parentage in the past. In a 2009 episode of the family's reality show Keeping Up With the Kardashians, she told her sisters, "I just can't believe that I'm really, like, legitimately part of this family," prompting Kim to joke, "I think Khloe's adopted!"

And when the socialite and TV star demanded to see her birth certificate, her mother stated, "Khloe is not adopted; she is just different in every way - different color hair, different color eyes, different color skin."

In the episode, Khloe tested her DNA with her mother's and they were a match - proving only that the youngest Kardashian sister is her mother's biological daughter.