Michelle William's beau Jason Segel "hasn't been this happy in forever."

The couple have only been dating for a few months, but it appears the relationship is getting serious already.

Jason is reportedly delighted with his and Michelle's relationship.

"Jason is totally smitten, [he] hasn't been this happy in forever," a source told People magazine.

"It's like the first girl he's ever been this way with."

Michelle and Jason made an appearance at an afterparty for the premiere of Take This Waltz at Sons of Essex restaurant in New York City Thursday night.

To onlookers the pair appeared to be incredibly in love with each other.

Jason, 32, and Michelle, 31, chatted with friends, laughing and holding hands. They had conversations briefly then left the event.

Michelle and Jason's romance seems to be going from strength to strength and the actor has already been introduced to Michelle's six-year-old daughter with the late Heath Ledger.

Jason is said to be working hard to bond with Matilda and is believed to be planning a future with the One Week with Marilyn star.