Wales international prop Rhodri Jones will join Ospreys from Scarlets on a two-year deal at the end of the season.
The 24-year-old has played in 13 internationals and signed a national contract in December 2014.
His new contract is with the Ospreys only, and not an extension of the national deal which was jointly funded by the Welsh Rugby Union.
The tight-head made his 100th appearance for the Scarlets in the win over Edinburgh on Friday, 12 February.
"We are disappointed to see Rhodri leave the Scarlets however we respect his decision," said Scarlets general manager Jon Daniels.
Jones said: "It was an honour to have played my 100th game for the Scarlets last weekend and I will give my all to the region as we challenge for a Pro12 play-off position from now until the end of the season.
|More from BBC Wales Sport|
|Ronnie O'Sullivan turns down 147 chance|
|France players confident, says Charteris|
|Ospreys' Webb a doubt for Edinburgh|
"I've enjoyed my time with the Scarlets but this is a great opportunity for me professionally. I'm very excited about this move."
Jones' chances have been limited at the region and the national team by the emergence of Samson Lee, who has established himself as Warren Gatland's first-choice tight-head.
His opportunities with Wales have also been limited by Exeter's Tomas Francis, who was selected for the World Cup squad and has made two appearances off the bench during the 2016 Six Nations Championship.
Ospreys rugby manager Andrew Millward welcomed the signing.
"Rhodri is someone with huge potential to become a quality player," he said.
"We see him as an individual who fits what we want from a tight head, in terms of ability and character, and we believe that we can work with him to keep moving his set piece work forward."