Cardiff Blues fly-half Rhys Patchell will join Welsh rivals Scarlets on a two-year deal from next summer.
Patchell, 22, will leave the Blues at the end of the current season after rejecting a new contract.
He will join Wales centre Jonathan Davies at Scarlets next term after Davies' switch from Clermont Auvergne.
"Rhys is an exciting young player who will bring a new dimension to our game next season," head coach Wayne Pivac said.
"He's been playing particularly well for the Blues in recent weeks. He will be joining what is shaping up to be a very exciting backline."
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Patchell made his regional debut for the Blues in September 2012 and his international debut for Wales in the summer tour to Japan in 2013.
"I'd like to thank Cardiff Blues for giving me an opportunity and supporting my development over the last few seasons," he added.
"As a Cardiff boy it has been a really difficult decision to have to make, and one that I have deliberated over for quite some time.
"I will continue to give my all to the Blues as we look to build on recent victories in both the Pro12 and Challenge Cup. I will leave the region with fond memories and having made lifelong friends."