The naked truth about Alec Baldwin's nude scene in his new movie, It's Complicated?

It's not his real booty!

The comedy centers on a divorcee (Meryl Streep) caught in a love triangle with her ex-husband (Baldwin) and a new love (Steve Martin).

In one scene, Baldwin is forced to strip down -- but director Nancy Meyers says he refused to bare his backside.

"He said, 'Mine's beautiful. However, I don't want to do that,'" she tells USA Today, adding that both she and Baldwin approved a butt double.