She hides her anger mighty well!

Angelina Jolie headed out for a day of shopping with daughter Vivienne yesterday, and she was all smiles despite the reports that Brad Pitt attended his ex Jennifer Aniston's 50th birthday party over the weekend. The two actresses have been longtime enemies, so that's gotta feel like a knife in the back.

Angie has reportedly not been too thrilled that her ex-husband is getting back on the dating scene, either!

A source tells X17:
    "Angelina was furious when she caught word Brad had been quietly dating Charlize Theron. She's massively threatened by her. Then she hears about him attending Jen's birthday party and totally lost it! Not because she's pining away for him, but rather because she thinks he's doing all of this to make her look stupid and stir up some headlines."

In the latest round of crazy rumors, the Malificent star has allegedly set her sights on Sean Penn in an effort to make Brad jealous.

"[Angie and Sean] have been flirting up a storm. They’ve met at least twice since Brad and Charlize’s dating news came out in the open. They were already pretty close, but they’ve decided to ramp things up since their exes got together," a source told NW.

And here we thought Brad and Angelina were going to live happily ever after!