Ryan scored 27 goals for the Diamonds in season 2016/17 before moving to East End Park and now returns to link up with Ian Murray's side, who are two points behind leaders Raith Rovers in the Ladbrokes League 1 title race.
The 25-year-old began his career with Hamilton Accies and had loan spells with Brechin City and Arbroath before moving to Forfar Athletic.
