Albion centre-half and player of the year Matt Upson has signed a one-year deal with Premier League newcomers Leicester City.
Upson, 35, was still wanted by the Seagulls but he has decided to join Nigel Pearson's Championship champions instead from July 1, once his one-year contract at the Amex expires.
His departure leaves managerless Albion with two recognised centre-halves, captain Gordon Greer and youngster Lewis Dunk, following Adam El-Abd's move to Bristol City in January.
Upson initially joined Albion on loan from Stoke in January 2013 before signing a one-year deal last summer.
He helped the Seagulls to the Championship play-offs two years in succession and was particularly influential this term under Oscar Garcia.
The former Arsenal, West Ham, Birmingham and England stopper made 43 league starts, more than any other player apart from Stephen Ward.
He was hampered towards the end of the campaign by an ankle injury sustained at Barnsley in April and missed Albion's second leg defeat in the play-offs at Derby County.