The relationship between their on-screen characters didn’t work out, but Mad Men co-stars Alexis Bledel and Vincent Kartheiser are excited to celebrate their real life engagement.

“They couldn’t be happier,” a friend of Bledel’s told Us Weekly. “Vincent proposed a few weeks ago,” said another source. “She’s been wearing her ring. It’s huge!”

The pair made their public debut as a couple back in October at an exhibit opening in New York.

In the fifth season of Mad Men, The 31-year-old actress plays an unhappy housewife who has an affair with Kartheiser’s character, ad exec Pete Campbell.

Bledel is probably best known for her role as Rory on Gilmore Girls. She dated another co-star – Milo Ventimiglia, who played Rory’s on-again, off-again boyfriend Jess on the hit series – for more than three years. Kartheiser, 33, was previously linked to actress Rachel Leigh Cook.

Congratulations to the happy couple on their engagement!