The Australian singer, whose wife Jules gave birth to their first son Hudson last month, said that when she was pregnant, the baby never kicked during his gigs.
Sebastian told The Daily Telegraph: "He didn't move, he did nothing. But then he went to a John Farnham concert and he was kicking like crazy. Maybe he's more a John Farnham fan than a Guy Sebastian fan."
The musician recently revealed that he wrote 'Big Bad World' about his son and hopes to have it finished in time for it to be a part of new album Armageddon.
"I wanted to finish it once he was out in the world," Sebastian said. "Writing a song for your baby is a bit clichéd, but it's what we do, we live our lives through song.
"It's about that promise we all make to our kids, but realise we don't have as much control as we think. We want to protect them from the big bad world, but the promise matters the most."
Sebastian said that he and Jules received lucrative "offers" from magazines to exclusively reveal photos of Hudson for the first time with them, but he said that they wanted to publish the pictures themselves.
He said: "I'm not opposed to people doing magazine stories. I've done them in the past, done the at-home story about us getting married. But this one, in particular, you have to hide your baby.
"Yeah, you can make a bit of cash, but you have to choose your moments. I couldn't be bothered. It was much easier just to get it out there. My fans really appreciated it; my whole career has been very public from the get-go, it's nice to share it."
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