Nobody knew it, but sitcom star George Lopez was hiding a secret health crisis. And in an incredible act of love and devotion, it was wife Ann who donated one of her own kidneys to save her husband's life.

Lopez underwent an extremely risky organ transplant surgery just last week after he and his wife, Ann, checked into a Los Angeles hospital.

For years, the Lopez family has kept secret George's medical condition, a genetic condition that was slowly deteriorating his kidneys.

"It's been a long road," Ann admitted.

Lopez has been a friend of "Extra's" ever since "The George Lopez Show" began. And in his memoir "Why Are You Crying?" George wrote about how his wife Ann actually proposed to him after meeting at a casting session.

Also in the book, George and Ann talk about a rough marriage early on, which included indiscretions on George's part.

But that's all in the past now, as George writes: "She is the person who through it all stayed true. Even in the darkest times she never broke."

But Ann isn't the only person Lopez wanted to acknowledge. "I want to thank Sandra Bullock," Lopez added.

Sandra, one of Lopez's executive producers on his sitcom, said this Tuesday about George and Ann's surgery: "The love and respect I have for Ann and George has doubled knowing how they have struggled with this quietly for the past several years."

George and Ann's book comes out in paperback in May.