The 'America's Got Talent' host – who became a father for the first time last month when the singer gave birth to their twins Moroccan Scott and Monroe – is amazed by how fortunate he has been in his personal life and says he has never been happier now he is a dad.
When asked if he wakes up in disbelief that Mariah is next to him, he replied: "Every single day. Every time - I - and especially now, because it's on a whole different level because it was like, 'Ooh, I have my dream girl and this is amazing.'
"But now, like, to actually have a family and to look down and see children that look like both of us, it's, it's surreal, man.
"I'm loving it, man. I can't stop smiling. It's an amazing thing to look down and see miniature yous looking up at you and stuff."
Nick explained Mariah has always been his "celebrity crush" and he was determined to be in a relationship with her and, when they met three years ago, was thrilled to find she was not the diva people had previously claimed.
He told TV talk show host Piers Morgan: "I mean, I've always loved her.
I've always been a huge fan. I would say I've spoken into existence because that was like my celebrity crush. And when I met her for the first time, I thought, 'Oh, I'm going to have to meet this diva and I'm going to have to do this.'
"I mean, she was so down to earth and so normal and so regular - and a lot like I was."