Leicester Tigers have agreed a deal to sign Scarlets fly-half Owen Williams at the end of the season.
The 21-year-old, who is in the final year of a development contract, has played seven times for the Welsh side's first team this term.
Scarlets coach Simon Easterby said he was "disappointed" at the manner of Williams' departure.
"Unfortunately, this sudden move came to us with no warning or discussion," said Easterby.
Williams is the second fly-half signed by Leicester for next season, following last month's recruitment of Ryan Lamb from Northampton Saints.
Williams, will join a strong team of international-class fly-half players at Welford Road including Toby Flood, Dan Bowden and Lamb.
Neath-born Williams has impressed everybody with the way he has stepped into the Scarlets fly-half role with first-choice and Wales star Rhys Priestland sidelined with an achilles injury.
He moves to pastures new with Priestland, new signing Steve Shingler, who returns to the Scarlets from London Irish in the summer, Aled Thomas and Dan Newton all recognised fly-halves in the Scarlets squad.
"We'd like to be clear that we had discussed a new contract with him, and made his representative fully aware of our willingness to discuss securing his future as a rugby professional with us," said Easterby.
"Unfortunately, this sudden move came to us with no warning or discussion and is a surprise to us in the context of what we would consider to be in the best interests for Owen going forward."
"Of course, Owen goes with our best wishes for the future and we wish him every success.
"He is still a young Welsh player with a lot to experience and prove and in making this decision we sincerely hope he gains a lot from his time at an English Premiership club."