Steven Shingler will rejoin Scarlets from London Irish at the end of the season.
The fly-half crossed the Severn in 2011 but returns in the summer on a three-year-deal.
Shingler's brother, Wales flanker Aaron Shingler, has also agreed a new three-year contract with Scarlets.
Head coach Simon Easterby said: "It's important for our progression to have secured these two talented players from our region who will add real value to our squad going forward."
Steven Shingler said: "I have had some great experience from my time at London Irish, and it's been good for me to play in the intensity of the Premiership.
"During my time at London Irish I've been lucky to work with and learn from some great people like Mike Catt, who have pushed me forward and improved my game.
"I am very grateful to have this opportunity to come back to Wales, and back to what I consider my rugby home, playing for a region I feel so strongly about."