The 36 year old, who plays Kimberly Crystal 'Kim' Day on the U.S. version of the TV sitcom, met actor Mikey Day, 28, when he was cast as her character's estranged husband, Craig Baker.
The pair's chemistry on camera carried on off-set - and they're now a happy couple in real life.
Blair says, "It's never happened to me before but it happened, I fell in love. I've never had a set romance. I think it makes work a lot more fun.
"We were really affectionate while we were shooting but we didn't get together until filming wrapped, because we didn't want it to be like, 'Ooh, what if you don't like me...?' (But) he's wonderful, he's so funny."