Frizell will fly to England with the Tongan side on Thursday for a historic three-Test tour against the Lions after previously representing Wales and Australia in what is a unique international treble.
"I am really proud to represent my mum (Sophia's) side of the family," Frizell said from the Tonga camp at Redcliffe on Tuesday.
Frizell had a conversation with coach Kristian Woolf about playing for Tonga when he first took over in 2014, but was committed to Wales, with whom he played in the 2013 World Cup.
The NSW Blues second-rower then won the 2017 World Cup with the Kangaroos, but last played for Australia in 2019.
Coach Kristian Woolf addresses the Tongan team during a training session at Redcliffe, Queensland.
"It has come full circle. To play for Tonga is something I always wanted to do, and I'd been speaking to 'Woolfy' over the last two years about it," Frizell said.
"This will be the first time that Tonga has been able to do this in a three-game series against England."
The Tongan pack will boast the likes of Warriors giant Addin Fonua-Blake, Manly wrecking ball Haumole Olakau'atu and South Sydney's Keaon Koloamatangi, who made his NSW debut this year.
Tonga reached the World Cup semi-finals in 2017 and the quarter-finals in 2022, and Frizell said they had the firepower to beat England.
"Why not? We are confident we can beat anyone," he said.
"A lot of these guys have paved the way for Pacific Islanders in terms of coming back and playing for their country.
"We continue to lead the way, and hopefully I can help create something for future Tongan kids aspiring to play for their country.
"It is a strong squad and I have a real spring in my step.
"It is not nice playing on the other side against these boys like Addin and Haumole, so it will be nice to stand alongside them for the first time."
Frizell said Tonga was on the cusp of something special on the international stage, like his club side the Knights, who stormed into sixth position after a slow start to make it to the second week of the NRL finals.
"(Winning the premiership) is what we want to do, and if we can put in another tough pre-season hopefully we can have a better start to the year, " he said.
Frizell is signed at the Knights until the end of 2024 and has an option in his favour for 2025 and a mutual option with the club for 2026.
He intends to play until he is 35.
"I'd love to play for as long as I can if the body and mind is good," Frizell said.
Tonga's three-Test tour of England kicks off on October 22 in St Helens.
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