Kim Kardashian Addresses Khloe's Biological Father Questions

Sources close to Kim tell TMZ ... the family is fuming at Robert's ex-wives ... who both told the tabloids Robert privately revealed that Khloe was fathered by another man.

We're told, "It's totally untrue and the family is very hurt." One source close to Kris Jenner tells us ... Khloe's mom isn't even fazed by the rumors because "it's so ridiculous, it's not even worth her time."