KHLOE KARDASHIAN is re­fusing to take a DNA test that would provide the irrefutable answer to THAT question – AND the truth could cost her a fortune, say insiders.

The 28-year-old reality TV star be­lieves that O.J. Simpson’s lawyer pal, the late Robert Kardashian, is not her dad, but she doesn’t want to find out for certain for at least another seven years, say sources.

Khloe, her sisters, Kim, 32, Kourt­ney, 33, and brother Rob, 25, were all left with a trust from Kardashian’s estate, but they can’t cash in until they turn 35. And Khloe is not about to kiss off easy money by discovering she isn’t rightfully part of the inheri­tance, note the sources.

Once she gets her share of the trust, Khloe can then use DNA testing to find out if the rumors are true – that O.J. is her real dad!

“Khloe knows everyone has specu­lated she is O.J.’s daughter,” said a family friend.

O.J. had an affair with Khloe’s mom Kris Jenner while she was still married to Kardashian, according to the family friend.

And The ENQUIRER recently pointed out that although Khloe doesn’t look like her sisters, there is a startling resemblance between her and the disgraced football star’s 26-year-old daughter Sydney.

Kris confessed in her memoir that she “fooled around” while married but never admitted to having sex with O.J. Meanwhile, the attorney and the football legend had been very close friends since the early ’80s and often partied together before Robert divorced Kris in 1989.

“O.J., his wife Nicole, Robert and Kris were all wild back then,” said the family friend. “Kris crossed the line and slept with O.J. more than once.

“It  was one of the main reasons Robert divorced Kris and blamed the whole thing on her.”

After talking to her mother about what happened, Khloe believes O.J. is her biological father and plans to eventually find out for certain, according to the family friend.

“She wants the absolute truth,” added the friend. “But she is very happy to remain a Kardashian until she turns 35.”