London - Wales centre Scott Williams is to leave PRO14 side Scarlets and join Welsh regional rivals the Ospreys on a three-year deal starting from the 2018/19 season.
The 27-year-old won his 50th Test cap when Wales were beaten by New Zealand at the weekend.
"I hope it goes without saying that this has not been an easy decision for me but ultimately I feel it is a move that is the right option for me at this time in my career," Williams said in a statement released by the Ospreys.
Williams made his Scarlets debut in 2010 before making a first Wales appearance the following year and going on to be part of two successive World Cup campaigns.
"Negotiations to retain Scott have been ongoing for some months, but today we can confirm he will be leaving us at the end of the season," said Scarlets general manager Jon Daniels.
"Sometimes, despite everyone's best efforts, a player decides the next chapter of his rugby career should be at another club."
Ospreys Samoa international centre Kieron Fonotia will head in the opposite direction next season when he links up with the Scarlets.