Speaking to 7News, Ken Thorpe said he had no idea his son was homosexual.
"It was a shock because we never had any inclination that Ian was that way inclined," Ken said.
"God loves Ian and we love Ian unconditionally and we will support him," he said.
Thorpe told his family just weeks before he confirmed his sexuality during an interview with Sir Michael Parkinson, which aired on Channel 10 on Sunday.
"I'm not straight. And this is only something that very recently, we're talking in the past two weeks, I've been comfortable telling the closest people around me exactly that," Thorpe told Parkinson.
Since the interview went to air, celebrities and other gay men and women have praised Thorpe for coming out.
The Voice coach and gay singer Ricky Martin tweeted: "Congrats to @IanThorpe! Brave man! Happy for you! Millions appreciate what you've done! Proud of you! #SelfLove"