But the most remarkable admission during today's widely-predicted announcement in Hamilton that he would return to the NRL in Australia via a lucrative stint in Japanese club rugby was that he was honouring a "handshake agreement''.
Williams, 26, said he didn't want to leave the All Blacks and the Chiefs, his table-topping Super Rugby team, but felt compelled to do so.
There was speculation that, with All Blacks assistant coach Ian Foster in attendance, Williams had pencilled an agreement with the New Zealand Rugby Union to return in 2014, but he denied that today, as did Foster.
"One day I would love to come back but in saying that I'm not going to hold my breath because there are some great players here coming through who deserve all that they get,'' Williams said. "I've chosen my path and now I've got to walk it.
"I didn't think I would love it as much as I have here. To be honest, I feel I've found my place here at the Chiefs, with the boys, but it just goes back to I've given someone my word.
This appears to be a different Sonny Bill Williams who walked out on the Canterbury Bulldogs for a rugby gig in Toulon, France, in 2008, only months after signing a long-term contract. That broken agreement, which resulted in a five-year ban from the NRL, was the last time he agreed to such deals. Now he and his controversial manager Khoder Nasser negotiate only one-year contracts. They feel it stops Williams for being taken for granted and drives up his value.
The handshake agreement was made before Williams joined Canterbury in his successful bid to make the All Blacks. Having secured a foothold on rugby during his time in Christchurch - he made the All Blacks' end of year tour after his handful of games for Canterbury in 2010 - he continued to make his mark with the Crusaders last year before taking his game to a new level with his move to Hamilton and the Chiefs.
Williams, who played 17 tests in an All Black career which included winning the World Cup, is a near certainty to join the Sydney Roosters after his 12-game stint with the Panasonic Wild Knights which is believed to be worth about $1.5 million. He will not play for the All Blacks in the Rugby Championship which starts in August.
Williams added: "It's a pretty difficult situation, but I just have to make the most of it. If all things go well I will be playing league next year. I can't start that with this [regret] at the back of my mind, I've got to start fresh and give it my all.''
Flanked by Chiefs coaches Dave Rennie and Wayne Smith, Williams showed his emotions as he reflected on his All Blacks career and time at the franchise.
Rennie said: "There's an impression that Sonny is bigger than the team or bigger than the game but Sonny is very much one of the boys and he is certainly loved by his teammates.''
Smith, a former All Blacks assistant coach who took Williams under his wing at the national team, said: "I've really seen Sonny develop over the last two or three years and wherever he goes, they're going to be incredibly lucky. He's shown ability to come up to an immense level really in a quick time in a sport he didn't know much about.''
Williams, the New Zealand heavyweight title holder, will probably box again in November - during the Panasonic season - and indicated he could return to the country of his birth.
"If I ever came back to New Zealand rugby I'd definitely come back to the Chiefs. Even if there was no money here I'd come back for free.''
- APNZ