Alexis Bledel and Vincent Kartheiser Credit: Michael Stewart/; Gregg DeGuire/FilmMagic

Alexis Bledel got more than a paycheck when she appeared on Mad Men.

The Gilmore Girls alum, 30, who played the sex-starved mistress of oily ad exec Pete Campbell (Vincent Kartheiser) for three episodes now has the actor all to herself in real life.

The two were seen smooching on a June 14 flight from NYC to L.A. (Since they both had middle seats one row apart in coach, he turned around to kiss her in front of all the passengers!)

"They have been dating for a few months," a source close to Kartheiser, 33, tells Us Weekly, adding that the actor saw Bledel's Off-Broadway show Regrets in NYC in late March. So what's the selling point?

"Vincent is smart and charming," continues the pal. "He's nothing like his character!"

In the past, Kartheiser has been linked to actress Rachael Lee Cook; Bledel dated her Gilmore Girls costar (and on-screen love interest) Milo Ventimiglia for more than three years.