Town have agreed a fee with Charlton for striker Darren Bent which will eventually total £3 million. The Blues will receive £2.5 million up front with a further £500,000 due on appearances for the Addicks and for the full England side, and have a sell-on.
Charlton have long been admirers of Bent and had a £3 million bid turned down last summer. Alan Curbishley's club always looked favourites to land the England U21 international, despite interest from Sunderland and latterly.
Chairman David Sheepshanks told the club site: "It is always sad to sell one of your homegrown players but this has become a necessity.
"Both the player and his agent have, for the last 12 months, declined to discuss any new long-term contract, other than if we were promoted.
"It is understandable that the player wishes to play in the Premier League, leaving us no alternative other than to realise maximum value through his transfer.
"Last summer we didn't sell Darren, instead taking a calculated risk in retaining him in the hope that he would score the goals to take us to the Premiership. It very nearly worked - but not quite.
"With just one year left on a contract, negotiations are tougher. However, after carefully considering the offer, I, along with the manager and the board, are satisfied that, while I think Charlton Athletic are getting a fine young player, we are getting full value in today's transfer market.
"I would like to thank Darren for everything he has achieved with this club and wish him every success for the future both with Charlton and hopefully England."
Bent, 21, made 141 appearances for the Blues, scoring 55 goals, having made his senior debut in the 3-1 away win in Helsingborg in the UEFA Cup in November 2001.