The groom-to-be, who plays advertising executive Pete Campbell in the hit drama series, began dating Bledel after she was cast as his onscreen mistress last year (12), and he turned to their colleagues Elisabeth Moss and Jessica Pare when it came time to pop the question.
Pare tells People.com, "It was purely comedic but he was giving (us) a facetious rendition of his planned proposal. We were like, 'Great! Let's do this one without cursing and without yelling!'"
Moss reveals the whole cast is excited for the odd couple: "They are such a yin and yang. I've known Vinny for 12 years and Alexis is just the sweetest. I've never seen Vincent like this. It is really cool."
And even Kartheiser's onscreen wife, Alison Brie, has sent her congratulations to the acting pair.
She says, "My Twitter feed was abuzz today with (fans) going, 'Oh my God'. I think everyone thought I was going to be very jealous but I'm excited for him for the record!"
Kartheiser and Bledel announced their engagement earlier this week (begs18Mar13). It will be the first marriage for both.