The Belgian side have announced the signing of the centre-back this evening.
As reported by The News, Burgess has penned a three-year deal with the Brussels-based outfit, with the option of an additional 12 months.
The popular defender leaves Fratton Park on a free transfer following Kenny Jackett’s side’s League One play-off defeat to Oxford.
Monday night’s penalty shootout loss at the Kassam Stadium proved to be Burgess’ final Blues outing after spending five years at the club.
The ex-Middlesbrough man made 210 appearances following his arrival from Peterborough in 2015, scoring 12 goals.
Burgess played key roles when Paul Cook’s men claimed the League Two title in 2017 and in last season’s Checkatrade Trophy triumph at Wembley.
This campaign, the 28-year-old has arguably played his best football during spell on the south coast.
His consistent performances saw him crowned The News/Sports Mail’s Player of the Season, having collected a massive 69 per cent of votes.
Pompey entered contract negotiations with Burgess over a new deal in January, although both parties were unable to reach agreement.
The Teeside University graduate instead lined-up a move to Royale Union Saint-Gilloise, who are owned by Brighton chairman Tony Bloom.
Nevertheless, Burgess remained committed to Pompey right until the end.
During lockdown amid the coronavirus crisis, he volunteered his time profusfely to help vulnerable residents across the area.
He was also key in persuading the Belgian second-tier outfit to grant him permission to play in the play-offs.
Burgess was unable to bring the curtain down on his Fratton career with promotion to the Championship, though, with the Blues being knocked out of the play-offs by Oxford.
Now his exit to the continent has been made official.