Gary Roberts has departed Pompey by mutual consent.
The Blues had been seeking to unload the creative midfielder following the arrival of Kenny Jackett as boss.
Now his exit has been agreed, bringing to a close two years on the south coast.
Roberts scored 20 goals in 80 appearances after arriving from Chesterfield in June 2015 for an undisclosed fee.
He was a key figure of the Paul Cook regime, last term scoring vital goals against Carlisle, Hartlepool and Plymouth in the charge to the League Two title.
However, despite contracted at Fratton Park for another season and eager to remain, it was clear he had no future with Pompey - and now leaves.
In a statement, chief executive Mark Catlin said: 'I’d like to offer my sincere thanks to Gary - both on a personal level and on behalf of everyone at the club.
'I hope that he will forever be remembered for what he achieved at Pompey, especially last season when we went on that fantastic run to win the title.
'His contribution over the past two years has been invaluable – he has been a fantastic player for this club. We all wish him every success for the future.'