Having attended the Shore School in North Sydney where rugby union is the sport of choice, Roberts-Thomson still managed to discover Australian Football and was an avid Swans fan.
So when the club came calling, he could scarcely believe he was suddenly rubbing shoulders with some of his boyhood heroes, including Paul Kelly and Wayne Schwass.
Since that time Roberts-Thomson has had some journey, most notably the 2005 grand final victory over West Coast, when the 194cm defender had perhaps his best game in Swans colours.
A key cog in the Swans' defense, Roberts-Thomson has also been used effectively in the ruck and up forward and has overcome some serious injury problems to be within reach of 150 games.
This Saturday night's match against the Crows in Adelaide will be game No.141 since he made his debut in 2003.
Roberts-Thomson is out of contract at the end of the season and talks are yet to begin on a new deal, but he is hopeful of playing out his entire career with the Swans.
"I'd love to be a one-club player. The Swans have been fantastic," Roberts-Thomson said.
"They gave me the opportunity to play senior footy and it's been a lot of fun.
"I was a Sydney boy growing up so I supported the Swans.
"Coming to the footy club where some of my idols played, in my first year Paul Kelly was here, Daryn Cresswell was here, Schwatter (Wayne Schwass), so it was 'wow, how special is this?'
"The team now is coming together quite nicely too and I'd love to be a part of it for many years to come."
While the 150-game milestone is on the horizon, Roberts-Thomson is loath to look too far ahead.
Past Achilles and foot injuries forced him to spend long periods on the sideline, while he missed half of last season and the opening six games of 2011 with an ongoing hamstring problem.
But he has been a key figure in an extremely successful period for the Swans and believes the club's rejuvenated young list could be about to embark on another exciting chapter.
"It's been a pretty special journey," he said.
"Starting out I didn't look too much into the future. The side was pretty successful when I played my first couple of games.
"We had Barry Hall, Leo Barry, Micky O'Loughlin all firing and in my first year we made a preliminary final against the Lions and were close to going through to the grand final.
"I've been fortunate to enjoy a fair bit of success at the club, 2005, 2006 playing in grand finals, being a part of that has been fantastic.
"Now seeing all the young guys come through is sort of like a new era.
"We've got a new coach and the boys are playing some good footy and everyone's really enjoying the unity we have at the moment."
Roberts-Thomson showed his versatility when used at full-forward in the Swans' round 11 thrashing of the Brisbane Lions.
He kicked a career-high three goals, demonstrating some previously unsighted tricks, including a neat fake and shimmy to bamboozle Lions defender Daniel Merrett and kick a goal.
"The boys certainly gave me a bit of grief over that," he said.
He still sees himself as a defender, but Roberts-Thomson is happy to play wherever he's required.
"It's tough to say," he said when asked his preferred position.
"At the moment things are going well for the team and I'm happy to fill in any position.
"But I suppose having played the majority of my career down in defence, I'm happy to play down there.
"It's always good getting forward and kicking a few goals here and there, everyone loves to do that, but at the moment I'm happy to play wherever the coach wants me to."
