The cage fighter - who was previously married to former glamour model Katie Price - is expecting his first child with the reality TV star and he has promised to help get her figure back once she gives birth.
He said: "Chantelle's been comfort-eating crisps, crumpets and chips and she's not happy about her figure. She doesn't feel sexy, but I find her sexier than ever - she really turns me on. I'm just trying to get her to believe it.
"After the birth, I'll help her train three times a week to get back into shape and try to help her eat healthier. And there'll be lots of sexercise!"
Despite having a failed marriage behind him, Alex is convinced he and Chantelle will go the distance.
He told Closer magazine: "Chantelle has helped me turn my life around. She's definitely The One. When she told me she was pregnant, it was the most amazing feeling in the world. My parents have just celebrated their 50th wedding anniversary I believe we can have a long-lasting relationship, too."