Clay Aiken finds it "heartbreaking" that his son has grown up so fast.
The 46-year-old singer has Parker Foster Aiken, 15, with music producer Jaymes Foster and explained that while he is "incredibly proud" to have seen what his little boy has become, it is somewhat upsetting because of how much children "change" as they age.
He told People: "I'd say the most wonderful part has been watching him grow into a young man. He is an incredibly respectful and smart and responsible young man, and that is something that I'm incredibly proud.
"But it's heartbreaking because they grow into little, mini adults and they change."
The former 'American Idol' winner - who was never romantically involved with best friend Jaymes but the pair decided to raise Parker together following an IVF conception - explained that he can see that his child is becoming more and more independent as time goes on and that he himself has had to learn how to change his attitude as a father as well.
He added: "It's heartbreaking to see the little kid change into a young man, almost adult who doesn't need me as much. But at the same time, you're very proud of the fact that he doesn't need you as much, right? It means you must've done something halfway decent.
"When he was a toddler, you have to learn how to be more patient. You have to learn how to be more selfless. And as they become teenagers, you have to learn how to let go in ways that you didn't
. "I'm very type A, I like to have control of what's going on around me. I've had to learn as he's gotten older that you have to be willing to let... I know that I have to let him become an adult and let him start to do more things on his own."
"I'm much more worried than I thought I was. I was not a horribly anxious person. I was not a person who worries. But now I check my phone when I see that he's in the car to see where he is and that kind of stuff. I mean, it's brought out some anxieties that I did not realize I had."
