Keiran Jack, the son of legendary Balmain rugby league fullback Garry Jack, is set to continue the family's proud sporting tradition - in the AFL.

Keiran, 18, was picked up by Sydney in Tuesday's AFL pre-season and rookie draft after impressing as a midfielder for the NSW-ACT Rams.

After playing representative rugby league in his early teens, Keiran stunned his famous father by turning his attention to AFL - and was rewarded with an opportunity with the defending premiers.

"It came down to a decision when I was 15, I had to decide what I enjoyed more and wanted to pursue at the time - for me it was always AFL," Keiran said.

"I think dad was a bit shocked but I think he's really enjoying it now.

"He's always been happy for me to do what I've been doing, as long as I enjoy it."

Keiran grew up with the sons of fellow Balmain league greats Steve Roach and Wayne Pearce and all three have gone on to enjoy successes of their own, albeit in different sporting fields.

Wayne's son Mitchell was an Australian schoolboys representative in rugby league and has been picked up by the Roosters, while Roach's son Dan is an up-and-coming union star after turning his back on league.

Garry Jack, who played 20 Tests for Australia and received the Golden Boot award in 1987 as the game's best player, said he couldn't be prouder of his son, despite his choice of sport.

"What do you do - make him sleep outside?" Jack joked about his son's decision to turn his back on rugby league.

"I couldn't push him to play league, but he'd be a pretty handy league player if he came back.

"He's done his own thing, he's worked very hard to be where he is at the moment and it's a full credit to him.

"He's done it on his own bat, he hasn't had any influence from me and he wouldn't want it any other way.

"At the age of 15 he said he just wanted to play Aussie Rules."

There is still a chance, however, that the Jack surname will continue in rugby league, through Garry's other son, Rhys, a member of Balmain's SG Ball squad. Another son, Brandon, has also shown potential aged just 11.

"They've told me they will keep going in league, they've promised me," Garry said.

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