AceShowbiz -

Alexis Bledel and Vincent Kartheiser, whose characters got involved in extramarital affair on AMC's series "Mad Men", are to tie the knot. Bledel's publicist, Meghan Prophet, confirmed the engagement news to Us Weekly. "They couldn't be happier," a friend of the actress says.

Kartheiser, who has been dating Bledel for about a year, proposed to the 31-year-old actress a few weeks ago. "Vincent proposed a few weeks ago. She's been wearing her ring. It's huge!" another source told the site.

The source added that Kartheiser had revealed his plan to propose to his girlfriend when the couple attended Amber Tamblyn and David Cross' wedding in October 2012. "He was saying [to fellow guests] they might elope and do parties in New York, L.A. and her hometown, Houston," the source revealed.

Kartheiser and Bledel were seen smooching on a flight from NYC to L.A. in June 2012. A source close to Kartheiser confirmed that they "have been dating for a few months" at that time, adding that the actor saw Bledel's Off-Broadway show "Regrets" in New York in late March. They finally made a public appearance in October 2012 when they attended The Macallan Masters of Photography collection opening at The Bowery Hotel, New York.

Despite their busy schedules, the couple have figured out how to keep the flame alive. "The most important thing for us is to make sure that we see each other in the flesh at least every 10 days," Kartheiser said. "I'm a really lucky guy!"

Before seeing Bledel, Kartheiser was linked to actress Rachael Leigh Cook. Meanwhile, Bledel, who starred in "The Sisterhood of the Traveling Pants", dated her "Gilmore Girls" co-star Milo Ventimiglia for three years until their split in 2006.