Britney Spears Claims to Have Made Out with Ben Affleck in Throwback Pic

Britney Spears just posted a throwback photo of herself and Ben Affleck from the summer of 1999 -- a time during which she claims they locked lips, which is ... random as hell.

The pop star threw up a pic of her, Ben and Diane Warren hanging out at a party -- one reported to have taken place in either June or July of '99 to celebrate her album '...Baby One More Time,' which came out that January.

No harm, no foul -- this photo of them has been circulating for years -- but Brit's new description of what she claims happened that night is interesting ... namely, that they kissed.

She writes, "Cool pic of me and Ben Affleck and Diane Warren years ago!!! He’s such an amazing actor. Did I fail to mention I made out with Ben that night … I honestly forgot ... damn that’s crazy !!!"

Britney continued ... "Wish I could tell you guys the story that happened before that !!! Oh dear, I’m just being a gossip girl. Psss I actually forgot!" She has since deleted the post.

Unclear why she took it down so quickly, but it raises eyebrows for obvious reasons. For one ... a love connection between herself and Ben has never been claimed by either one of them until now, and it's truly coming out of nowhere -- with no evidence to back it up either.

Fact is ... Britney spilled her guts in her memoir last year on everything from an abortion she says she had, to alleged infidelity and lots of other stuff about Justin Timberlake.

If this did in fact go down as she suggests ... wouldn't she have put it in the book???