The couple met on the set of movie thriller Case 39 in 2006 and they have been dating for more than a year.
They reportedly moved into a multi-million dollar mansion in Pacific Palisades, California this summer (10), but both actors have kept the details of their relationship quiet.
Cooper has now spoken publicly for the first time about his "love" for Zellweger and how much he enjoyed spending time with her on set.
He tells Entertainment Tonight, "I can't say enough about her. I just love her.
"I (loved) coming to work. I love acting with her. I can learn so much from her."
The Bridget Jones's Diary actress adds, "(He) is a great, great actor. I just got so excited, not believing that I was going to go to work with him."