Wales backs coach Rob Howley has been sent home from the World Cup for an alleged breach of World Rugby's laws covering betting and anti-corruption.
The 48-year-old's departure is a huge blow just six days before Wales' opening game in Japan against Pool D opponents Georgia.
A Welsh Rugby Union statement said Howley had "returned to Wales to assist with an investigation".
The WRU confirmed it was in relation to a potential breach of betting on rugby.
World Rugby's regulation 6.3.1 reads: "No connected person shall, directly or indirectly, bet and/or attempt to bet on the outcome or any aspect of any connected event and/or receive and/or attempt to receive part or all of the proceeds of any such bet and/or any other benefit in relation to a bet."
Wales have sent for Stephen Jones to fill the gap left by Howley's sudden departure and Jones is expected to arrive "imminently" at the squad's Kitakyushu base.
Former Wales and British and Irish Lions fly-half Jones has already been confirmed as the next Wales backs coach under Wayne Pivac, who will take the reins from Gatland after the tournament.
- Skipper Jones, Owens and Davies vital for Wales - Warburton
- Wales' Wainwright set to start against Georgia
The WRU statement said: "Rob Howley has returned to Wales to assist with an investigation in relation to a potential breach of World Rugby Regulation 6, specifically betting on rugby union.
"The decision was taken to act immediately in light of recent information passed to the WRU. No further details can be provided at this stage as this would prejudice the investigation.
"If required an independent panel will be appointed to hear the case. Rob has co-operated fully with our initial discussions.
"Warren Gatland has consulted with senior players and Stephen Jones will be arriving in Japan imminently to link up with the squad as attack coach."
Howley has been an integral part of boss Warren Gatland's backroom team since the New Zealander took charge.
The ex-Wales and Lions scrum-half was already set to leave his role after the World Cup.
Howley had been linked with the Italy head coach job with current incumbent Conor O'Shea expected to depart next year, but that now looks unlikely.
The former Wales scrum-half has been part of Gatland's backroom staff since being appointed in January 2008 and was one of the first backroom recruits, and also played under him at Wasps.
Since he became part of the coaching set-up, Wales have won four Six Nations titles, including three Grand Slams.
Howley was in charge of Wales' 2013 Six Nations success when Gatland was away on a British and Irish Lions head coach sabbatical.
He was also part of Gatland's winning Lions coaching team in Australia in 2013 and the drawn series in New Zealand four years later.
Michael Owen, former Wales captain, speaking on 5 live:
It's sad that Rob's got caught up in this, he's been a tremendous coach for Wales and this is the swansong for the Wales coaching team. It's a big blow for everyone involved, and for Rob Howley on a personal level.
I think the team will be affected. They're lucky to have Stephen Jones, he's an incredibly positive person and influence. He's someone who could come in and have a positive impact on the camp straight away.