25-year-old Tu'inukuafe has enjoyed a meteoric rise in rugby since his debut for North Harbour in 2015. His advancement in the 2017 Mitre 10 Cup under coach Tom Coventry and form as a replacement for the Chiefs led to his selection for the All Blacks this year.
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"It is exciting for my family and me to be coming home. I think we have a strong squad for next year. I have my Harbour coach Tom Coventry coming in to take the forwards and I get to stay in the region," said Tu'inukuafe.
"The set-up at the Blues looks great and I am going to enjoy being part of this club and hopefully I can do my part in helping the club do well."
Tu'inukuafe has struck up a strong relationship with Blues prop Ofa Tuungafasi in the All Blacks and is keen to be part of a maturing forward pack at the Blues, he said.
"Karl has been one of the real finds in New Zealand rugby in the last couple of years, and will only get better and better," said Blues coach Tana Umaga.
"He will be a really strong addition to our pack and gives us real depth in our front row with the likes of Ofa and Alex Hodgman. While Karl is comparatively new to the sport at this level, he will provide leadership to our young front rowers emerging in the club."
All Blacks Head Coach Steve Hansen said Tu'inukuafe's recommitment to New Zealand was fantastic news for New Zealand Rugby.
Tu'inukuafe has enjoyed his time at Harbour and wanted to stay loyal to the Mitre 10 Cup side that gave him his opportunity, and the coaching support he received there.
North Harbour CEO David Gibson said: "We are thrilled how it has worked out for Karl and his family. The 2018 season has been huge for Karl and his rise from Takapuna Rugby Club to the All Blacks has been amazing to watch. Our community is delighted to have played some part in that journey. We know Karl will continue to be a massive part of Harbour, both on and off the field, over the next few seasons."
The former Wesley College player moved to North Harbour in 2015 and also had a stint for Narbonne in France. In this time the former security guard shed over 35kgs to impress in Harbour's successful 2017 season that saw them make the semifinal in the Mitre 10 Cup.
He was called into the Chiefs pre-season as a replacement, before his call up to the All Blacks, with a debut off the bench against France in June.
The emotion of a Test debut...#SteinlagerSeries #NZLvFRA ???????? pic.twitter.com/MD7ZHUFRvh— All Blacks (@AllBlacks) June 9, 2018