Webb, who is on a National Dual Contract, will join an undisclosed French club for the 2018/19 season.
In line with our intention to keep our best players in Wales, every effort to retain the player has been made. Whilst the news is disappointing there is an understanding that on occasion market forces will make this impractical.
All parties would like to thank Rhys for his contribution to the game here in Wales and continue to wish him well for the future.
Webb said: “It’s a huge wrench to be leaving the Ospreys after spending all of my playing career with the team. I have made lifelong friends on and off the pitch and I cannot speak highly enough of the quality of the coaching team, players and all of the staff involved within the Ospreys organisation.
“I will continue to give the region everything I can to make sure we have the best season possible and I would like to conclude by saying a heartfelt thanks to everyone within the Region for helping me achieve my goals within rugby
“I would like to thank the WRU and the Ospreys for their efforts during this process.”
This statement was issued jointly by the WRU and Ospreys rugby.
