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While Mapu grew up half a world away from Northampton, he followed Saints with intense interest.
The Pisi brothers, Ken and George, who were part of Northampton’s 2014 title-winning side are two former Samoa internationals he knows well.
“I was born and raised in Samoa, but when I moved to New Zealand for high school, I stayed with the Pisi brothers and their family,” he said.
“We know each other really well, their parents gave me brilliant advice all through my junior rugby career, and Ken and George used to give me Northampton kit to wear when I was training – which I loved.”
Saints director of rugby Phil Dowson says the club believes Mapu can “thrive” in the Premiership.
“He is extremely physical, aggressive, and athletic, with a lot of raw talent and potential,” Dowson said.