Adam El-Abd has left Albion to join Bristol City for an undisclosed fee, signing a three-and-a-half-year deal with the Robins.
The move ends a 20-year association with the club: the 29-year-old Egyptian international joined Albion's then Centre of Excellence at the age of ten in 1994.
He signed professional forms in 2003, shortly after making his senior debut under Mark McGhee, and his final appearance - as substitute for David Lopez against Birmingham was his 300th in league football for the club.
In total he played 342 senior games, scoring seven goals, but having seen first-team opportunities limited the last two seasons, due to the form of captain Gordon Greer and former England defender Matt Upson, El-Abd has opted to depart to pursue his desire of more regular first-team football.
Albion chairman Tony Bloom paid tribute to the wholehearted central defender, saying, "Players of Adam's calibre in terms of loyalty to one club are a rare breed in the modern game. He has given us many years of service having come through the youth set up and has earned his place in our history books.
"He has risen with the club, helping us gain promotion to the Championship via the play-offs in 2004 and as champions in 2011, when he also won the player of the year award, and he has risen to many challenges under a number of different managers.
"I'm sad to see him leave, but he is the type of player who wants to be playing - particularly at this stage of his career. He lives for 90 minutes on the pitch and always gives 100% to the cause. I've no doubt he will prove a fine acquisition for Bristol City.
"He has given excellent service to the club and has been one of our most successful home-grown players. On behalf of all at the club, and all Albion fans, I would like to thank Adam for outstanding service and wish him the very best for the future."
Head coach Oscar Garcia added, "We wanted to keep Adam in the squad but we understand his position: at his age, he wants to play every game"
"He has been a great player for this club over many years, and I would like to thank him for his hard work since I arrived. We all wish him well for the future because he deserves it"
Watch El-Abd's tribute video on Seagulls Player