Mad Men’ co-stars Alexis Bledel and Vincent Kartheiser engaged

Vincent Kartheiser and Alexis Bledel at the Screen Actors Guild Awards in Los Angeles. Chris Pizzello / AP file

Their "Mad Men" characters had an ill-fated affair, but off-camera, Alexis Bledel and Vincent Kartheiser are excitedly celebrating their engagement, Bledel's rep confirms exclusively to Us Weekly. "They couldn't be happier," says a pal of the "Gilmore Girls" alum, 31, and Kartheiser, 33.

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Last June, Us broke news that the twosome -- Bledel played the mentally imbalanced mistress to his character, ad exec Pete Campbell -- had been "dating for a few months."

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Says another friend: "Vincent proposed a few weeks ago. She's been wearing her ring. It's huge!" In the past, Kartheiser has been linked to actress Rachael Leigh Cook; Bledel dated her "Gilmore Girls" co-star (and on-screen love interest) Milo Ventimiglia for more than three years.

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"They are so cute together!" another source tells Us of the spouses-to-be. It will be the first marriage for both, who attended the October nuptials of Bledel's "Sisterhood of the Traveling Pants" co-star Amber Tamblyn and David Cross.

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