With mostly family members in attendance – no Mad Men men or women – the wedding will take place at an undisclosed location on the East Coast, Arend, 31, told PEOPLE Thursday night in New York at the Cinema Society and Brooks Brothers screening of his bittersweet romance, 500 Days of Summer, which stars Zooey Deschanel.
Hendricks, meanwhile, said of her bridal gown: "I'm wearing Carolina Herrera. It was the first dress I tried on and it was magnificent."
And though Hendricks and Arend don't know whether they'll have time for a honeymoon, they like the idea of Tuscany. "A farm house, small car," he says, "something romantic."
Met Through CostarThe couple were introduced by her Mad Men costar Vincent Kartheiser. "It was not a set up," she insists. "We were all going to an event one night and another friend of mine said, 'You're going to like this guy.' "
The first date took place at the Magic Castle in Hollywood – with Kartheiser in tow. "We were just hanging out," says Arend. "And I realized that the day before a friend had told me I was going to like Christina. Halfway through the magic act, I looked at her and said, 'I'm supposed to like you.' And she said, 'You're Geoffrey? I'm supposed to like you, too.' "
Word spread. "We kept telling friends, 'I met this really cool person,' " he recalls. "But we never thought it was a love connection until the third date. We were at this bar in L.A. called The Prince. We kissed. And it was all over."
Romantic Proposal"I proposed under a chandelier that I retrieved from a restaurant called Il Bucco on Bond Street in New York," says Arend. "She had wanted [that particular chandelier] since she saw it when she was 22 years old. And now it's hanging in our dining room in L.A."
When Hendricks realized he was about to propose, he remembers, "She started bawling, and then I started."
And what will make him a great husband? "Everything," says Hendricks. "He's considerate, he's thoughtful, he's smart, he takes care of me. He's not full of himself. He's very, very giving."