Cameron Cowell signed a permanent contract with the club to stay at Castle Park after two loan spells with the Knights.
The full-back has been on loan with Doncaster from the start of the 2018/19 campaign and first arrived in a previous short spell on loan from Newcastle Falcons last season.
The 23-year-old has 20 appearances for the Knights last season and has scored five tries.
Cameron also played 38 matches for England World Cup sevens, where he made nine tries and added a further 32 conversions.
Blessed with pace and lighting feet, Cameron can play at either wing or full-back and spent time in the London Irish academy as a youngster.
The London-born back scored three tries in an impressive first spell at Castle Park will look to make the 15 jersey his own for the 2019/20 season as a permeant signing.