This means that Ipswich will recieve £2.58 million because of the 20% sell on clause when Bent signed for The Addicks.
"I'd like to place on the record my appreciation for Darren's efforts on behalf of the club over the past two seasons," said Charlton plc chairman Richard Murray.
"He's been a model professional during his time at Charlton. He has been a pleasure to work with and has always represented the club magnificently, both at domestic and international level."
He added: "Realistically, it was always going to be difficult to hang on to a player of his quality following relegation, but we feel we have negotiated the best deal possible for the club and, after a payment to Ipswich, it's a sum of money that will cushion the effects of relegation for the club."