Wales prop Rhys Thomas is to join the Scarlets from Newport Gwent Dragons at the end of the season.
The 19st 11lb 26-year-old tight-head has played 119 games for the Dragons since his debut around six years ago, and seven times for his country.
Scarlets head coach Nigel Davies said: "We're delighted to have signed Rhys. He will add strength and skill to our pack as we prepare for a big season ahead.
"Importantly, he adds to our pool of Welsh talent and I know that his workrate and power will make him a favourite with Scarlets supporters.
"He's determined to progress as a Heineken Cup and international player so I think we can expect big things of him in 2009-10 and beyond.
"We're firming up the look of the squad for next season with plenty for supporters to look forward to. Our future is all about responsible decisions on the playing side and cementing a balanced squad that can perform well in Europe. To do that, we've made it a priority to strengthen key areas of our group with quality players. Adding Rhys to our line-up, is a good example of that."
Thomas, who started Wales' 20-15 RBS 6 Nations win in Italy, said: "It was a pretty easy decision to join the Scarlets; they're a region with a strong tradition of being successful and they have a group of talented players and coaches. I'm friendly with a good few of the players having been in the Wales squad with them - we get along well.
"A major factor in my decision was Parc y Scarlets; it's a great stadium with superb training facilities on site. The indoor training centre on site is amazing.
"I've worked with Nigel Davies before, when he was part of the Wales set-up, and I'm greatly looking forward to working with him again on a daily basis.
"It's my aim to help get the Scarlets back into the later stages of the Heineken Cup and perhaps, to winning the Magners League. I think that being at the Scarlets will also help me push ahead with my international ambitions.
"Newport RFC, the Newport Gwent Dragons and the Rodney Parade crowds have been good to me; they've been a huge part of my life for eight years and I've had a great time there. I've played a lot of games there and have made a lot of friends. I wish them all the best for the future."
England's preparations for the Autumn International series were potentially dealt a further blow as Maro Itoje was forced to undergo an x-ray after Saracens' European victory over Scarlets on Saturday night.