28/03/2012 12:15 BST | Updated 28/03/2012 12:30 BST

Michelle Williams And Jason Segel Dating?

Michelle Williams has reportedly found love with her pal Jason Segel.

Michelle and How I Met Your Mother star Jason are said to be "smitten", according to Us Weekly.

"They are smitten and very serious," a source said. "She hasn't been this happy in a long time."

The couple have been spotted on a string of dates in recent weeks and were snapped taking a romantic stroll after dining together in Brooklyn last week.

An eye witness told the mag: "He put his arm around her and made her laugh as they walked," says a witness. "[They] seemed very relaxed."

Jason has also proved to be a hit with Michelle's six-year-old daughter Matilda, who he was seen bonding with last Sunday as she went for a scooter ride.

The pair are thought to have met through Jason's Freaks And Geeks co-star Busy Phillips, who just happens to be BFFs with Michelle.

“Michelle and Busy have a mutual girl crush on each other,” a source told The Enquirer. “They’re soul mates who do absolutely everything together.

“Lots of people whisper behind their backs, speculating that their relationship is more than just platonic. But they’re just the best of friends.”

Michelle previously dated Heath Ledger, but split with him five months before his death in 2008.