Ospreys number eight Morgan Allen will join Scarlets for the 2015-16 season.
The 25-year-old has made 53 appearances for Ospreys since making his senior debut in the 2010-11 season.
Scarlets head coach Wayne Pivac said: "He is a strong ball carrier and will add another dimension to our back-row.
"Morgan has plenty of rugby left in the tank and will no doubt learn and continue his development under the leadership and guidance of experienced guys in our squad like John [Barclay]."
Allen is the second number eight to join Scarlets recently, with Jack Condy signing from Cross Keys the previous week.