We bet there's a couple reasons for this.

Jennifer Garner headed to exercise class this morning in Brentwood, and we couldn't help but notice that the actress has lost A LOT of weight since announcing her decision to divorce Ben Affleck. While she has been working out every day, we think a lot of her slim down has to do with the stress of her former husband moving on so quickly with his mistress Lindsay Shookus.

The mother-of-three is said to be "hurt and humiliated" by the Batman star's decision to make his new romance so public, and it's pretty obvious it's taking its toll on her physically.

"Things are getting ugly between the pair. Ben is no longer hiding his relationship with girlfriend Lindsay, and Jen has hit a breaking point. Jen’s never been about getting retribution.That’s not her style. But Ben’s insensitive actions have changed her. Jen is finally realizing; she could never really trust Ben," a source dished to Life & Style.

The only thing that could make things worse for Jen would be if Ben and Lindsay decide to have a baby!