Bella-Kotchap moves to Serie A Verona on-loan with an option to buy at the end of the season.
The defender joins for an initial €500,000 loan fee with his permanent option set at €7m.
Bella-Kotchap leaves St Mary's after a difficult 12 months in England, where he made five appearances for Saints last season.
The previous year, Bella-Kotchap played on-loan with PSV Eindhoven.