Steve Hansen has revealed the best athlete he ever coached in his illustrious rugby career spanning 24 years.
The former All Blacks coach was spoilt for choice with players he mentored as an assistant from 2004 until 2011 and as the head coach from 2012 until 2019, with the likes of Richie McCaw, Dan Carter, Kieran Read and Keven Mealamu - among many others - enjoying stellar careers under him.
But speaking to The Daily Telegraph in Australia, Hansen labelled former All Black now Sydney Rooster Sonny Bill Williams as "a freak" and "the best athlete I ever coached".
"The greatest rugby player I've coached was (Richie) McCaw but Sonny would be the best athlete I've coached from a pure athlete sense," Hansen said. "He's a freak of nature."
Hansen mentored Williams in the All Blacks in two separate stints between 2011 and 2019. He stepped down from the role after last year's World Cup, which Williams competed in, with 93 wins in 107 tests – an 87 per cent winning rate, the best by any rugby coach with at least 15 games under their belt.
He also described Williams as a "role model."
"Sonny is 35 now but he's been an active athlete for a long time and he really looks after himself. He's a freak of nature," Hansen said.
"There is no reason, as long as he stays injury-free, that he won't do the job. He had been out of league for a while before coming back and going to Toronto, but he's just such a good athlete.
"As he has got older, he has matured. His training habits and his off-field habits are world class now. He will be a good role model for the young 'fellas' in the club."
Williams was a part of New Zealand's World Cup wins in 2011 and 2015, coming off the bench in both finals. Against Australia in the 2015 decider, he executed a pivotal play - offloading to a rampaging Ma'a Nonu who beat a handful of defenders to score, handing New Zealand a comfortable 18-point lead early in the second half.
Hansen said that pass was a perfect example of why Williams is so impressive.
"That is the sort of thing he can do, can't he? He can do things other people can't do."
Williams' unique combination of strength and skill has made him one of, if not the, greatest rugby code-hopper, with titles in the NRL and world rugby coupled with mesmerising performances.
"There are a lot of similarities (between rugby league and union). You have that rushed defence and a shorter offside line than we have so you can learn things from that," Hansen said.
"They are two different games but the fundamentals are the same."
Williams has 118 NRL games to his credit and 24 tests with the Kiwis, as well as 58 test caps with the All Blacks. During his time with the Crusaders, Chiefs and Blues in Super Rugby, he gained 61 caps.
Hansen said he keeps an eye on the NRL and will watch Williams' return with keen interest. Tomorrow night will mark the 35-year-old's first match in the competition in six years, where he is set to come off the bench in the Roosters grand final rematch against the Raiders in Canberra.
Meanwhile, Hansen said with no All Blacks games on-field yet, he feels no sense of loss having stepped away from coaching. A Bledisloe series and Rugby Championship have both been discussed between respective Sanzaar unions for 2020, but nothing has been finalised.
But Hansen expects if there is an All Blacks game soon, he will feel it.
"I'm sure there will be a tug in the old heart when they finally get out onto the track. But Fossie [Ian Foster] will do a great job with them I'm sure, and I'm really excited for him to take the team to the next level.
"It will be exciting to watch."