Prince: I'm His Long Lost Son

Prince has a biological son who is not mentioned in the probate case ... at least according to the alleged son.

Carlin Q. Williams of Missouri is 39 years old and filed legal docs claiming his mom met Prince in the lobby of the Crown Center Hotel in Kansas City, Missouri back in July 1976. She says in an affidavit she drank wine with the singer and checked into a room and had unprotected sex.

According to Carlin's mom, Marsha Henson, she didn't have sex with anyone 6 weeks before and didn't have sex with anyone during her entire pregnancy.

Carlin -- who is currently in federal prison for gun possession -- now wants an order testing Prince's DNA samples against his to unlock the mystery.