Tana Umaga has made the surprise decision to step away from professional rugby coaching to focus on his new family business.
Umaga only last year re-signed with the Blues as defence coach, but has since had a change of heart.
The former All Blacks captain was head coach of the Blues from 2016 before transitioning to his defence brief under Leon MacDonald in 2018.
Outside the defensive duties, Umaga has been a major mentor in Rieko Ioane's ongoing transition from wing to centre, and would have been an invaluable sounding board for Roger Tuivasa-Sheck's code switch that is expected to begin with Auckland this weekend.
Earlier this year Umaga and documentary-maker wife Rochelle launched a supplement range that harnesses traditional Māori and Pasifika ingredients for wellness products under the brand Viktual+.
For now at least, that will be his focus.
"I've absolutely loved my time at the Blues, but ultimately my family comes first and, with that in mind, I have decided to put my time and energy into growing our business alongside my wife Rochelle," Umaga said.
"We are excited about what the future holds for our business, and although I'm stepping away from rugby, I know the door isn't closed and who knows what the future holds. I'm grateful to the Blues and NZR for their understanding and support as I embark on a new chapter."
Blues chief executive Andrew Hore said the club will sorely miss Umaga's presence but were fully supportive of his decision.
"Tana has been a massive part of the Blues for the past six years. His influence on the club and the team has been significant. He has excelled in his current role of defence and has been an integral part in developing and driving the culture within the team and our club," Hore said.
"We had hoped he would continue in the role for the next couple of seasons, but we respect his decision and why he has a desire to try something new, and we wish him, and Rochelle, all the best. Our door will always be open for Tana and his family."
Under Umaga's guidance the Blues this year recorded the highest tackle accuracy and conceded the least tries to lay the foundations for the club's first major title in 18 years when they won the Super Rugby transtasman title.
Blues head coach MacDonald said that while Umaga has been outstanding as a defensive coach, his influence within the overall team and the club has proven pivotal.
"Tana has developed into a mentor for so many of our players and his leadership into the development of our identity and our culture has been inspirational. His influence throughout our club, on and off the grass, has been crucial to where we are today and I am sure we would love to see him return in the future.
"No doubt we will be reminding our 2022 group of the high standards that Tana has set for them as players and as people."
NZR general manager professional rugby Chris Lendrum said Umaga's contribution had been considerable.
"Tana is one of the greats of the game in New Zealand. He has huge mana and respect in our rugby community, and he has taken the leadership and knowledge he showed as a player and enhanced it further in his coaching with Counties Manukau in the NPC, the Blues in Super Rugby and for our New Zealand Under 20s and Māori All Blacks.
"We wish him and his aiga all the best for the next phase of their lives. I'm sure he won't be lost to rugby and we hope to see him back."