Nick Cannon says Mariah Carey is the ''hardest working woman'' he knows.

The 34-year-old star has posted a touching tribute to his estranged wife, who he split from last summer after six years of marriage, on Instagram to help promote her upcoming album, 'Mariah: #1 to Infinity,' referring to her as ''the queen.''

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

Rumours have been swirling that the former couple, who have three-year-old twins Monroe and Moroccan, are trying to rebuild their relationship since the 'America's Got Talent' host recently admitted Mariah would always be ''the love of my 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.''

Mariah, who has never commented on their split, also recently hinted Nick would be joining her in Las Vegas, where she is set to kick off her residency at Caesars Palace next month.

Asked if her children would staying in the city, she said: ''They're always with me. They're with me or they're with their father. It is what it is and I would never just be like, 'I'm going, you're not going to be with me.' They wouldn't understand that. So they're the most important thing to me. Their family is going to be here. They're going to be great. They do their own thing.''