The look of love!
Williams, 31, hit the premiere of her new film Take This Waltz at the Tribeca Film Festival in NYC Sunday. Though she walked the red carpet solo, Segel, 32, "snuck through the back entrance to be there with Michelle" during the screening itself, an eyewitness tells Us.
The cautious new duo also made it a point to enter the Abe & Arthur's afterparty separately -- but once inside the Heineken-sponsored bash, "There was no mistaking that they were a couple," the witness shares. "They seemed very comfortable and happy to be there celebrating together."
Adds the source, "Michelle seems completely enamored by Jason."
Segel, for his part, seems equally taken with the My Week With Marilyn star; earlier this month, the actor was spotted in L.A. with sweet photos of Williams taped to the back of his iPhone.
Though the pair has only been dating since February, they've known each other for years through Segel's Freaks and Geeks costar--and Williams' BFF--Busy Philipps. "They're much more serious than everybody thinks," a source close to the couple tells Us. "They're really happy!"