The chart-topping pop star has enjoyed huge success during his time in the music business, but has now suggested he's actually quite a shy person.
"I'm an introvert and don't do parties unless I'm paid to or I have to promote something," the singer told Us Weekly.
Williams, 50 - who first found fame as a member of the boy band Take That in the 90s - loves watching and listening to podcasts when he's at home.
"All I do is listen to and watch podcasts," he said.
"Right now, I'm back on the UFO and paranormal trail, so that's where I get all of my entertainment needs, (including) finding out what the drones are in New Jersey."
A pop star worldwide, Williams loves nothing more than listening to podcasts when he's at home. (James Ross/AAP PHOTOS)
The Let Me Entertain You hitmaker also revealed he's still prone to feeling starstruck.
"I always get starstruck around comedians - like Will Ferrell, Adam Sandler and Chris Rock - and also Brad Pitt," he said.
"Movie stars (have) a quality that is unusual, beguiling and magical, but at the same time means nothing. It's so strange. And it's not their fault."
Robbie released his own Netflix documentary back in 2023, but the pop star previously admitted that he struggled to actually watch it.
The award-winning star revealed how tough it was reliving some painful moments from his life.
"It was deeply unpleasant, to be honest with you," he told The Project.
"I think that people don't even like looking at selfies of themselves and hearing their own voice.
"And if you multiply that by watching you descend into mental illness and agoraphobia and depression and anxiety and you are watching a nervous breakdown, it's not a normal thing to do."