Jennifer Morrison and Jesse Spencer dish on their romance and his Parisian proposal

House costars Jennifer Morrison and Jesse Spencer got engaged over the holidays, but Spencer had been trying to propose for six months.

“She’s just so frickin’ smart, and I didn’t want her to have any inkling that it was about to happen,” Spencer, 28, tells the summer issue of InStyle Weddings.

First he planned to pop the question on vacation in Costa Rica – but Morrison, 28, got sick. Then they went camping in Big Sur, but “We were freezing the whole time,” Morrison says – not exactly romantic.

Finally, on a trip to Paris, Spencer took Morrison to the Eiffel tower, where he handed her a box containing a ring and said: “Veux-tu m’épouser?

There was just one problem: “I was like, ‘Uh, what are you doing?’ ” Morrison says. “He said, ‘I’m asking you to marry me in French!’ I was just staring at him. I don’t speak French. And he said, ‘Well, are you going to answer?’ And I replied, ‘Oh, yes! Yes! Yes! Yes! Yes!’ ”

They will wed this year, although they won’t reveal the date. But the 200-guest event will take place under a tent at a private L.A. estate, with Morrison wearing an empire-waist, dark ivory Elie Saab gown.

The couple met in 2004 on their way to shoot the House pilot. At first they dated secretly, but after four months, they quietly told their suspicious castmates they were, in fact, an item.

Working together and having a relationship hasn’t been a problem. “It’s nice to have your best friend with me every day,” Morrison says. “He not only gets it, he’s part of it.”

Want to read more engagement tales? See our Real Life Weddings blog.