Charles Piutau idolised the late New Zealand rugby legend Jonah Lomu, who had attended the same school as him, and on Saturday he gets his first taste of the tournament that the former All Black lit up.

Like Lomu, 31-year-old Piutau donned the All Blacks jersey, winning 17 caps, but when he was omitted from the ultimately victorious 2015 World Cup squad he upped sticks and moved abroad.

Eight years on it is the shirt of Tonga, the land of his parents' birth, he will wear with the daunting challenge of upsetting the world's top-ranked team, Ireland, in Nantes.

Piutau, who is also known as Salesi Piutau, is able to represent Tonga due to a change in World Rugby's eligibility rules.

One of 10 children -- five girls and five boys, with the boys sleeping in the garage adjoining the family house -- Piutau went to the famed Wesley College where Lomu's presence was felt everywhere.

"For all the kids that went to Wesley College, you knew that Jonah went there," he told AFP on Tuesday at the Tongan base in Rueil Malmaison outside Paris.

"You knew that when you went to the dining room you had all his jerseys and team photos, the All Black jersey, he was in the Wesley jersey."

Piutau, who due to his all-round skills can slot in at fullback, centre or wing, said he knew what position he wanted to play as soon as he entered the changing room.

"In the locker room (Lomu) had his name on the number 11 jersey and so I wanted to play wing," said Piutau.

"I played 11 for the school at the time just because of him.

"He was a massive influence."

- 'A real credit' -

Lomu -- who scored 15 tries in two World Cups including four against England in the 1995 semi-final -- died aged 40 in November 2015, a few weeks after he had watched the All Blacks beat Australia in the final.

"I met him a couple of times," said Piutau.

"He kind of knew who I was because of playing there (at Wesley).

"The thought of him recognising you or shaking your hand... he was one of my idols growing up.

"What an impact he had on the game."

Piutau says he has no regrets about ending his All Blacks career by moving first to Wasps in England and then Ulster and Bristol but concedes he never imagined he would play in a World Cup for Tonga.

"I think at the start of my rugby career in New Zealand I didn't think that I would be putting on the Tongan jersey knowing the eligibility rules at the time," he said.

"Definitely it is something that I always wanted to be a part of; a World Cup is the pinnacle of our game.

"Now to be here years later, older but still feeling like a young kid the excitement levels are sky high.

"I can't wait to get stuck into them."

Piutau is also happy to help give Tonga a chance to shine in front of a global audience.

"There is an opportunity to represent this Tongan jersey, what it means to us to put our mark out there in this competition and for Tongans worldwide to see and hopefully be proud of," he said.

Assistant coach Zane Hilton said Piutau's value to the squad was priceless.

"It is a real credit for someone to say he makes other players round him better and he is a great example of that," said Hilton.

Piutau has been fortunate too to have "a lot of insight" from his elder brother Siale, who captained Tonga before retiring from Test rugby in 2019.

"He’s always been someone throughout my career that I have been able to use as a sounding board and ask questions," Piutau said.

As Piutau has travelled the world, he has accrued a global property portfolio.

Before settling on rugby, he had wanted to be a carpenter or a builder but he feels his body is going "to be a bit too sore" when he hangs up his boots.

His eldest brother Hakaei, though, chose the other way round.

"We swapped. I was probably lucky," said Piutau with a grin.

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