The couple began dating last year (12) after meeting on the set of the hit U.S. Tv show, and now the actors are set to wed.
A representative for the beauty has confirmed the news to Us Weekly magazine, and a source tells the publication, "They couldn't be happier... Vincent proposed a few weeks ago. She's been wearing her ring. It's huge!"
This will be the first marriage for both - Bledel, 31, previously romanced her Gilmore Girls co-star Milo Ventimiglia, while Kartheiser was last linked to actress Rachael Leigh Cook.