Nick Cannon will ''forever be in debt'' to Mariah Carey.

The 'America's Got Talent' host paid tribute to his estranged wife - who he split from last summer after six years of marriage - for being a ''wonderful and nurturing'' mother to their four-year-old twins Moroccan and Monroe.

Taking to Instagram on Mother's Day yesterday (10.05.15), he wrote: ''Gotta represent for the Mother of my children. She is such a wonderful, thoughtful, festive, loving and nurturing Soul. I will forever be in debt to you for blessing me and the rest of the world with Roc & Roe.

''A true #Queen. Will love you always @MariahCarey #HappyMothersDay.(sic)''

The post came just a few weeks after 34-year-old Nick described the 'Hero' hitmaker as the ''hardest working woman'' he knows.

Alongside a photograph of the 45-year-old beauty's new album ''Mariah: #1 to Infinity', he wrote: ''#1ToInfinity album in stores May 6th. #TheQueen #NoHate #HardestWorkingWomanIKnow (sic)''

And Nick recently described his estranged spouse as the ''love of his life''.

Asked if he would consider reuniting with her, he said: ''It's one of those things, I'm a hopeless romantic too. Through this learning process, you never say never.

''To me one thing I know, that will always be the love of my life, always be my family and that's never going to change.''