The two only began dating after filming for the television season had wrapped.
"We were completely professional. We never saw each other out," Kartheiser said. "We never -- it was nothing, it was just work."
"I did know he liked her from a very early point," actor Jon Hamm said. "I was a supporter of that union."
Creator Matthew Weiner agreed.
"Honestly, they're a really good match," he said. "They're both very down to earth, with a sense of responsibility and strong family ties. And they've been acting since before they can remember, which makes for a very special personality. It's not just that I thought they would look cute together."
"Even with all of Alexis's amazing qualities, I think that if she had not been such a good actress, he would not have been interested," he added.
Bledel and Kartheiser got engaged in March 2013.