Before his shock departure last Saturday, Williams had barely been on speaking terms with Folkes but after learning that his star player, who turned 23 yesterday, had flown out of Sydney to take up a lucrative rugby union deal in France, the Bulldogs mentor sent him the text message.

In it, he told Williams the bold move was "the worst decision of yr life", warned he would lose "the respect of everyone" and suggested the Kiwis superstar had put money ahead of his "integrity".

Folkes also declared he was "lost for words" by Williams's actions and advised: "I cannot stick up for u on this one".

Despite saying "you hav allowed others to run yr life", he finished by telling Williams he "alone" was "accountable".

The message, obtained by the Herald , provides a clear insight into the mood of Folkes, who told Williams he felt "betrayed personally".

But the Herald can reveal that Williams's relationship with Folkes had been strained for some time and in an interview earlier this year he said that the coach rarely spoke to him - despite his standing at the club and in the game.

One of the more in-depth conversations he had with Folkes was when the coach approached him after an article incorrectly speculated that he was set to become a muslim after dumping his agent Gavin Orr for Anthony Mundine's manager Khoder Nasser. After asking if the story was true, Folkes told Williams it would be a "joke" if he converted to Islam and advised him to stay away from Mundine.

It is understood Folkes's comments were raised by Williams's camp during a meeting with Bulldogs officials at a Brighton restaurant in June.

Asked about the Williams text message, Folkes said: "The fact he is prepared to forward what is supposedly a private and confidential text message reinforces that he has gone off the rails, in my opinion.

"I got a response but Sonny wouldn't want that response printed and I'm not going to give it to you. The fact that he is prepared to toss that up to a paper, I think, is a pretty ordinary thing to do.

"On the back of what he has done it confirms there is something wrong with his head."

With Folkes announcing earlier in the year that he would stand down at the end of the season, Williams hoped Stephen Kearney would be appointed as his replacement and if the New Zealand coach had been given the job there was a good chance he would still be at the club.

The opportunity to play under the coaching of Tana Umaga, the first player of Samoan heritage to skipper the All Blacks, was a significant factor in his decision to quit the Bulldogs to play rugby union for Toulon.

Umaga spent three days with Kearney in Melbourne last month and told the Storm assistant coach of his plans to poach Williams.

"He [Umaga] got me a little beauty," Kearney said of his 1991 Junior Kiwis teammate. "I was certainly aware of his interest in Sonny and he was here doing the sly. Tana was upfront with me.

"He said, 'I've spoken to Sonny's management group', and he made sure to keep me in the loop of what was going on."

Having been helping to mentor Williams, Kearney said he was aware of "private" issues that contributed to his decision to walk out on the Bulldogs.

"If Sonny hadn't been in a position he was in, I'm not too sure he would have made that move to Toulon," Kearney told Fairfax's Sunday News in New Zealand. "Had a few other areas in his life been more settled, we probably wouldn't be talking today about it.

"I could sense his frustration with a few things when we talked.

"As a friend, those issues are between him and I and that's how they should stay.

"I'm not saying what he did was the right thing to do but he is a young guy … and we have to look at exactly why he made this decision.

"I think he was dealing with a lot of issues and I don't think his situation is over."