Michelle Williams and Jason Segel are reportedly "smitten and very serious" with each other.

The Hollywood pair are longtime friends but have recently become romantically involved, according to reports. Michelle and Jason were spotted strolling arm in arm after a meal in Brooklyn over the weekend.

"They are smitten and very serious," a source told US Weekly.

The alleged couple were seen enjoying each other's company on March 24. After dining at Frankies Spuntino on Saturday night, Jason was spotted entertaining Michelle with his comedy as they strolled around.

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

On Sunday, Jason was pictured bonding with Michelle's six-year-old daughter Matilda as she went for a ride on her scooter.

Logistically, it is difficult for the pair as Michelle is based in Brooklyn while Jason calls Los Angeles his home. However the two are reportedly "trying to make it work".

"She hasn't been this happy in a long time," the source added.

Michelle split from actor Heath Ledger shortly before his death in 2008. The pair have daughter Matilda together.

Jason, 32, has previously being linked to Lindsay Lohan.