Jack Osbourne believes aspects of fatherhood are "impossible to comprehend."

The son of Sharon and Ozzy Osbourne and his fiance Lisa Stelly welcomed daughter Pearl last month.

Jack was in awe when he first laid eyes on his baby girl.

"People say when you have a kid it's like instant love, but unless you've experienced it, it's impossible to comprehend," he told the British edition of Hello! magazine. "The moment I saw her I felt more love than I'd ever felt for anything. It was the weirdest, most overwhelming thing."

Jack, who had been dating Lisa for three months before she conceived, acknowledged the gravity of becoming a father from the outset.

"I think I responded with 'that's interesting' [when Lisa first told me she was pregnant]," he revealed. "What do you say? If we'd been trying for two years, of course you'd be like 'awesome'. But we met in May and found out in August. I told Lisa: 'you need to give me a week to really take this in'. I had that time to get my head around the whole situation."