The music mogul launched her career and married the 'Hero' hitmaker before divorcing in 1997 and Tommy admits with the benefit of hindsight that they shouldn't have wed.
He said: ''I have no regrets but looking back it would have been better to maintain a professional relationship. But you can only go forward.''
Asked if it is strange to see her as a judge on 'American Idol', he added to People magazine: ''No it's fun to see people morph and experiment.''
Tommy was married when he first met Mariah and he recently revealed everyone was against their relationship, even his therapist.
An extract in his memoir reads: ''You don't understand [I told the therapist]. Mariah is going to be the biggest star in the world. She's going to be bigger than Michael Jackson.
''I can only wonder about the expression on my therapist's face when she saw Mariah thank God for that first Grammy and then Tommy Mottola for believing in her. She could no longer call me delusional.''
When Mariah, 42, wanted to take some time out of her career at the age of 21, Tommy, now 63, stopped her.
He explained: ''My feeling was that there'd be plenty of time for Mariah to celebrate just a little ways down the road. I'm not talking 10 years, just a few.''