Charlton Athletic have agreed an undisclosed compensation package with Premier League side West Ham United for midfielder Diego Poyet.
The 19-year-old, who came through the Addicks' academy, was offered a new contract at The Valley but he turned it down, instead choosing to leave the club at the end of June when his existing deal expired.
Poyet, who made his first-team debut in January, was named the Sky Bet Championship side's player of the year last season.
Addicks chairman Richard Murray told the club's official website: " I can't say we are happy with the outcome because our aim from the moment we started negotiating with Diego over a new contract in early 2014 was to keep him at the club in the long term.
"We take pride in seeing players learn their trade in the academy before going on to become regulars for Charlton's first team.
"That has been the case for a number of years and has never been more evident than last season when five academy graduates, including Poyet, made their senior debuts."