Tonga's 30-12 opening-round win over England has put them in contention for the World Cup semi-finals and a possible clash with Australia.
Keaon Koloamatangi says he hopes Tonga succeed if Australia does not win the tournament.
Koloamatangi represented Tonga 10 times, including at the 2022 World Cup, before switching to Australia ahead of last year's Ashes tour.
The 28-year-old will play prop against Fiji at Suncorp Stadium on Sunday night and join St George Illawarra from South Sydney next season.
He said representing Australia was an opportunity he could not refuse and fulfilled a childhood dream.
Koloamatangi said the decision did not mean he valued one side of his heritage over the other.
"I'm just as Australian as I am Tongan. I was born Australian and my dad's Tongan."
He said Tonga coach Kristian Woolf respected his choice and added, "He was respectful and accepted my decision. I have no regrets," Koloamatangi said.