Britney Spears' former dancer -- who Kevin Federline claims hooked up with the pop star while they were dating -- is addressing the media "Circus" around her ... though she's keeping tight-lipped about the exact nature of their relationship.

Britney Spears and Kevin Federline are in an all-out war after the father of her two kids has unearthed sharp claims in his memoir, “You Thought You Knew” (out Tuesday) — alleging his ex-wife was physically and verbally violent with their sons and even used cocaine while breast-feeding.

Just before her ex-husband's memoir was officially released, the "Crossroads" actress took to Instagram to share a photo that featured her riding on horseback. She is turned away from the camera and appears to be shirtless. In her lengthy caption, Britney begins by dressing the movie "Maleficent," calling it an "incredible movie."

Britney Spears’ “Circus” is hardly her most iconic music video, given the clips she released for “…Baby One More Time” and “Toxic.” Regardless, a famous political organization called Spears out for alleged cruelty on the “Circus” set.

Britney Spears brought the crazy back in 2007, after her Fairy-Tale-in-Opposite-Land marriage to second hubby Kevin Federline broke up. While the world watched, she shaved her head and wrote "666" on her dome, allegedly attempted suicide and had everybody ...