Grey's Anatomy star Katherine Heigl was shocked to find out her co-star T.R Knight was gay - because she had spent the show's pilot flirting with him.

The Knocked Up actress, who married singer Josh Kelley (below) last December, was a single gal when shooting began on the hit medical drama in 2005.

That said, a handsome co-star caught her eye.

The actress' romantic plans didn't going anyway - her lustful looks were ignored as it turned out T.R. Knight (dating Mark Cornelsen at present) is gay. She says:

"When we were filming the pilot I was single and so was he and I kind of had my eye on him. I was getting nowhere and I was super-confused. I was like, 'Hello? Do I have something hanging out of my nose? Why aren't you paying any attention to me? Needless to say, it quickly became a friendship once he told me."

Funny stuff. In the end, it all worked out, as Katherine Heigl ended up with a great husband in Josh Kelley and a best friend (on and off the show) in T.R. Knight.

Steve Marsi is the Managing Editor of TV Fanatic. Follow him on Google+ or email him here.