SHOCK VIDEO: Britney Spears SEXTAPE Leaks . . . And Brit Brit . .. Is RIDING HER MAN . . . Like She's At A RODEO!! (She's NOT . . . That . . . Innocent)

Britney_Spears_Cakes2 learned that a Britney Spears SEXTAPE just leaked - and it's VERY GRAPHIC.

The video, which VIEWED, but we do not have nor has ever possessed - shows Britney "riding" her man - who is filming the whole thing.

In the video, the 35-year-old mother of two is smoking what appears to be a JOINT while she's riding the "D" too.

Brit was putting in WORK too. We ain't seen hips move that well . . . since SHAKIRA!!!

We're not gonna post a link to the vid here (We don't want that SMOKE). But it's out there - and maybe someone in the comments below will post it.