"He was definitely smitten with her from the beginning," says the source."But he asked his friends for advice, and they told him to play it cool because he'd just got out of a long relationship.

"I was really nervous," Alexis said in an AMC Q&A about her sex scenes with Vincent.

"[Vincent] noticed, and made it much better for me by just sort of making sure I felt comfortable.

He kind of helped me take the edge off a little bit just by being nice." Vincent's on-set attentiveness paid off. "They're both great people; he's nothing like his character on the show." Alexis couldn't agree more!

"He's light and funny and has lots of energy on set," she's said. Very, very different than Pete." Let's hope Vincent and Alexis' relationship lasts much longer than their on-screen fling!

So he and Alexis spent some time together at viewing parties for the premiere and events in New York and really hit it off, and by June he was telling friends they were dating." And Vincent isn't the first co-star Alexis has romanced.

She once famously dated her Gilmore Girls co-star Milo Ventimiglia.

“Mad Men” co-stars, Alexis Bledel and Vincent Kartheiser are madly in love.

The couple, whose characters had a disastrous on-screen affair, are happily engaged in real life, Bledel’s rep confirmed with Us Weekly.

Meanwhile, Kartheiser previously dated actress Rachael Leigh Cook.

Together for more than a year now, the duo may have been bitten with the marriage love bug after attending Bledel’s “Sisterhood of the Traveling Pants” co-star Amber Tamblyn’s wedding in October.

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.