The 47-year-old brunette beauty went public with her new squeeze at the premiere of his HBO show The Newsroom and the two were affectionate and kissing on the red carpet.
The Social Network screenwriter, 51, and Kristin looked like a happy couple as they smooched in front of the cameras.
Kristin was all smiles in her aquamarine dress and pink heels for the premiere and Aaron was in a dashing suit.
Aaron has a 12-year-old daughter Roxy and Kristin adopted her daughter Gemma Rose last year.
A few years ago Kristin spoke about marriage saying: "I don't know if I'll ever get married. I don't say never, but I just might not. I'm 44, but I think you can have what you want no matter how old you are!"
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