The 23-year-old, one of many key players in the Kirkcaldy side’s strong quest for promotion last season, has announced on Twitter that he was moving on from the Stark’s Park club.
He said: “Time to move on, loved every minute of my time again at Raith Rovers
"Promotion back to the Championship, third-place finish, play-off semis – been the best time I’ve had so far.
"Can’t thank everyone involved with the club enough – the best people in every department, and the fans. All the best.”
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Armstrong joined Rovers in November 2018 after spells at Wolverhampton Wanderers, Dunfermline Athletic (on loan) and Ross County.
His departure from Stark’s Park came very soon after two other prominent players headed through the exit door – defenders Kieran MacDonald and Fernandy Mendy, who were themselves on their way shortly after part-time player David McGurn.