Wayne Smith says he knows deep inside the time is right to finish up with the All Blacks.

One of the great love affairs of New Zealand sport is coming to an end. Wayne Smith is finally ready to call time on a remarkable 20-year relationship with the All Blacks team he still adores with all his heart.

Yes, "the Professor" is about to lock away his secret formulae and hand his defence clipboard on to a new appointment who will be identified in coming weeks. The 60-year-old rugby treasure will be succeeded, but never replaced. Not after 20 years building the intellectual property, drive and passion that has become an intrinsic part of making the All Blacks one of world sport's most successful and recognised properties.

Smith on Friday announced he would be finishing up as an assistant coach with Steve Hansen's All Blacks at the end of the Rugby Championship, and spoke exclusively to Stuff about his reasons for walking away now, halfway to a possible unprecedented hat-trick of World Cup titles.

One thing you can be sure of. Smith does not end this incredible 20-year relationship – five as a player, and 15, over three stints, as a coach – without having thought the decision through. He loves his wife Trish and twin sons Nick and Josh dearly. But his beloved All Blacks come a close second.

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"Everyone understands this is a pretty high-pressure job – the stakes are high, the scrutiny is high, and it's the sort of job you take seriously," he began when asked two simple words: 'why now?'. "The jersey is like a precious jewel to me and you've got to keep shining it. To do that you've got to stay hungry and if I'm honest with myself I'd say I'm losing a bit of that absolute hunger and drive that the job demands.

"You can be assured I've got enough for the next few months but I don't want to get to the point where it becomes a drag..

"I see it as a win-win. It's a win for me and my family to step away a wee bit. But I think it will be a win for the All Blacks too. It's a chance to get one of these great young coaches we've got coming through to add a bit of freshness and hunger."

It really will be the end of an era. As much as Steve Hansen has become the driving force of arguably the greatest international sporting team on the planet, Smith is in many ways its heart and soul. Certainly its tactical acumen.

He is the only current coach to have pulled on the famous black jumper, having played 17 tests among 35 games in total for the All Blacks as a fleet-footed first five-eighths from 1980-85. He is also the mastermind behind a defensive system that denies tries as efficiently as the team scores them, and is known far and wide for his innovative thinking and ability to speak to the players in their language.

He is the Yin to Steve Hansen's Yang. The Robin to the Gaffer's Batman.

Hansen tried his best to deflect Smith's D-day, basically refusing to contemplate the prospect with his longtime sidekick (the two joined forces as fellow assistants with the All Blacks in 2004, but go way back to the days when Smith was player-coach of Canterbury B and Hansen was his skipper).

"I knew it was time to let him finish when he asked my wife to convince me to stop pressuring him into re-signing," acknowledged Hansen. Eventually even he got the message.

"It's fair to say I'm retiring from the All Blacks after a third of my life spent in black. It's been a huge privilege, I've taken it seriously, and it's been a massive passion of mine. At some stage you've got to finish, and this is my time," adds Smith.

He isn't ruling out further involvement in rugby after a hiatus to tick off a few key things in life. But he swears by two guiding lights: it won't be with the All Blacks, and it most certainly won't be against them.

"There are a lot of things I want to do," says Smith. "I want to reconnect with some people, I've got a grandson and I want to spend time with the family, we'll do a wee bit of travel, and I'll probably do a couple of projects ... but essentially it will be time to refresh.

"I've got no interest helping other teams try to beat the All Blacks. I've told [NZ Rugby chief executive] Steve Tew and Steve Hansen that. I will do some stuff in rugby but it won't be with tier-one teams competing against the All Blacks."

Smith said he hadn't agonised over his decision, merely followed the advice of someone he respects immensely. "[Former All Blacks scrum coach] Mike Cron once tell me that when you know you've got to leave the police, you don't want to leave it a year because it's a year wasted. You've got to go when you know the time is right and I'm pretty sure it's my time."

Tew, who flew in from Japan for the announcement, said Smith "has made as great a contribution to the legacy of the jersey and everything it stands for as anyone else in the modern game".

Hansen called Smith "a very special man" and added: "He has an unrelenting passion for the game, he's always been innovative, prepared to speak his mind, and he's never allowed himself to stop learning."

Smith, who will help with his successor's transition during the Rugby Championship, said he never figured he'd achieve his All Black dream as a player when he moved (from his home in Putaruru) to Canterbury to further his career, let alone play such an influential role as a coach.

"I was able to achieve something I was in awe of but which I grew to love. It's hard to put into words how much it means and how much it shapes your life."

Smith was "really proud" of what he had achieved with the All Blacks and name-checked Hansen, Tew, long-time influence Gilbert Enoka and Sir Graham Henry as people who had influenced him hugely.

"They're courageous, they're brave in their decisions, they're challenging, they're excellent, and they're team-first people. We tried things, and we took chances. We have been a group that has challenged the norm and I think the legacy is in a good place."

So, a sad day or a happy one for Wayne Smith?

"As you think about what a significant part of your life it's been, of course there's sadness. But if you know deep inside it's the right thing, you can't stay sad for long. You know the team is going to keep forging on and I'm going to get a lot of enjoyment out of watching them ... from the other side of the fence."

WAYNE SMITH

Born: Putaruru

Played: Canterbury, All Blacks.

Tests (1980-85): 17

Coached (professional era): Crusaders 1997-99; All Blacks assistant 1998-99; All Blacks coach 2000-01; Northampton 2001-04; All Blacks assistant 2004-11; Chiefs assistant 2012-14; All Blacks assistant 2015-17.