https://www.bbc.co.uk/sport/rugby-union/49733089
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 not been found guilty (yet) of breaching the regulations - but sending him home like that implies he is.
It will probably damage Wales' chances in the RWC. Splitting up the 'Band Of Brothers' coaching team must be very disruptive, but just maybe there is a silver lining with Stephen Jones stepping in to replace him. Jones doesn't have the experience or inside knowledge and continuity, but he is fresh and has done pretty well so far after finishing playing - and he gets to work with and learn from Gatland (as a coach) before taking over permanently as backs coach next year.