Carey divorced the former Sony Music executive in 1998 and waited ten years to walk down the aisle again with current husband Nick Cannon.
The 'Butterfly' singer explained that she was "afraid of the concept of marriage" following her public separation from Mottola, but credited Cannon with helping her trust again.
"This is a different situation and… I'm a different person. It's a different time in my life. And nobody will ever be able to steal my spirit again," Carey told 20/20. "So I'm just happy to be in love and to be here. When he's nice, he's the best guy in the world."
Carey also discussed her struggle to give birth to the couple's twins Moroccan and Monroe after previously suffering a miscarriage.
She admitted it was "tough" to undergo a variety of fertility treatments, but said she was so thrilled when the twins were finally born.
"They're incredible… [And] I will say that they really respond to music," Carey commented.
This week, the couple released the first pictures of Moroccan and Monroe.
Carey and Cannon's full 20/20 interview with Barbara Walters airs Friday at 10/9c on ABC.
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Watch a preview of Mariah Carey and Nick Cannon's 20/20 interview below: