Credit: Steve Granitz/

Mariah Carey takes her fitness seriously!

Hubby Nick Cannon said the mother of 4-month-old twins, Moroccan Scott and Monroe, is working hard at getting her pre-baby body back.

"She's so focused right now on every aspect. She's going to come back and knock out the world," he told Us Weekly Wednesday at the America's Got Talent finale in L.A. "She's getting in shape." 

Cannon, 30, said his 41-year-old wife has worked hard to get her post-baby where she wants it to be. "At two months she was walking around in a bathing suit," he said. "Every day she's just killing it. I personally think she's going to come out looking better -- looking like it's 1990! I think that's what she's aiming for, and I think she'll reach that goal." 

So do the duo ever work out together? "We do, but she's too serious!" Cannon said. "She works out in the water. I don't like the water. I can't swim that well." 

"Obviously [she pays attention to her] diet and eating properly," he added. "She does long, long hours on the treadmill. It's all doing it the right way."