Actor Neil Patrick Harris told David Letterman that he and partner David Burtka attempted to get knocked up.

Harris, the star of CBS' How I Met Your Mother, and celebrity chef Burtka entered a California domestic partnership in 2004. The couple welcomed twins Gideon Scott and Harper Grace, who were born via a surrogate, on October 12, 2010.

During an appearance on CBS' The Late Show, Harris showed off a holiday-themed calendar that featured Gideon and Harper to the audience's delight.

When Letterman stated, “When you think about it, birth the typical, traditional way is a miracle. But no less a miracle is this procedure when you consider,” Harris responded: “Well, I will tell you. You have to be very committed to wanting to have kids. Because you have to go through the financial hoops, you have to go through the health hoops, choosing the right egg, and doing all that. So, yeah, you can't just accidentally get knocked up one night. Believe me, we tried.”

“What?” Letterman said. (The video is embedded in the right panel of this page.)