TMZ has learned ... the chick currently kicking it in the Bahamas with Charlie Sheen was kicking it with someone else just two months ago -- Shifty Shellshock from the band Crazy Town.


Sources close to Charlie's "goddess" Natalie Kenly -- one third of Charlie's Bahamian threesome -- tell TMZ that the 25-year-old used to date Shifty on-and-off for about a year ... but the ex-couple finally called it quits a couple months ago.

Natalie also posed naked in a photo with Ron Jeremy -- we're told it was snapped back in 2009 ... during an AVN porn party in Vegas. Shocker.