Shaun Edwards will not become head coach of Wigan Warriors as planned at the end of the Super League season.
Edwards, 52, was presented to the media in August 2018 when he talked of "testing himself" in league, having coached exclusively in union.
However, after a successful Six Nations campaign as part of Warren Gatland's Wales coaching team, Edwards is expected to remain on the staff.
"I will not be taking up the head coaching role at Wigan," Edwards said.
"The reason is my lack of preparation. World Cup preparations have been brought forward a month and, as a result, I will be unable to spend eight weeks in Australia as planned on rugby league.
"I feel Wigan need a more experienced rugby league head coach than myself, to give the club and the people of Wigan the best team possible."
The first signs that Edwards would not return to his boyhood club surfaced earlier this year when he confirmed there was not a written contract in place for him to join Wigan - only a verbal agreement.
Edwards, who played in all eight of Wigan's consecutive Challenge Cup wins and featured in every game of every round between 1988 and 1995, was part of Wigan's late 1980s and early 1990s dynasty in which he lifted every available honour.
However, his last involvement in rugby league came with London Broncos in 2000, and that inexperience in his old code has prompted the U-turn.
Warriors chairman Ian Lenagan added: "He clearly feels that he is not the best man to take the team forward currently and I have to respect and accept this.
"Like every Wiganer, I wanted Shaun to lead the team and this very honest admission has taken me by surprise. I have always admired Shaun and I wish him well with whatever he does next."
What next for Wigan?
Wigan appointed former player Adrian Lam as an interim coach for this campaign, to fill the gap before Edwards' anticipated arrival in 2020.
Ex-Papua New Guinea international Lam, who took over from club legend Shaun Wane after a Grand Final-winning campaign, has had a tough start, with Wigan 10th after seven defeats from 10 games.
"For us now our next steps are to confirm the coaching structure for 2020 and beyond," Lenagan said. "We need to draw a line under the last few months and give our loyal fans the clarity they deserve.
"I'd like to thank our supporters for their patience and understanding in what has proven to be a very difficult situation to navigate and now we can concentrate on building more strong foundations to drive this wonderful club forward. We will announce our plans in due course."
'Statement a piece of diplomacy' - analysis
Dave Woods, BBC rugby league correspondent
Most Wigan fans have been pretty certain for some time that Shaun Edwards would not be returning to the club next year.
He appeared at a press conference last August to be unveiled as head coach from 2020 on a three-year deal but recently it has been shown that all was not as it seemed.
Edwards has been dropping lots of hints that he wanted to stay in rugby union.
He revealed he had not signed a contract with Wigan, that he was open to offers from anyone in union or league and that he wanted to repeat the successes he has enjoyed in international rugby union.
For Wigan fans, that was a show of great disrespect to his home town club.
The statement today that a lack of "preparation time" means he won't be coming back to Wigan reads like a piece of diplomacy aimed at saving some face for both him and the club.
At least now Wigan can look for a new permanent coach for 2020 now this mess has been concluded.
The question will now arise over the future of Adrian Lam. Success this year would put him in prime position to continue his role as head coach.
But the way the season has begun, Wigan have struggled. Lam will rightly point to a number of injuries amongst key forwards as being one major factor, but Wigan will hope to announce an appointment for next year soon.
And there is no certainty that Lam himself will want to stay anyway. He has family back in Australia, is living over here on his own, and initially stated he was happy to spend only one year in England.
Whether he and the club change their minds on that commitment remains to be seen.