The 20-year-old measures in at a whopping 6 foot 4 and has already made 18 outings in the Premier League following his 2014 debut.
But it appears the youngster isn’t a part of Claude Puel’s plans next season, with the Saints sending him out on loan to the Ewood Park outfit.
And the season-long move has now been confirmed by the Lancashire side, who will be looking to gain promotion to the Premier League this season.
Coincidentally, Gallagher bagged the winner against Blackburn in last season’s final of the Under-21 League Cup.
His departure leaves Charlie Austin, Shane Long and Jay Rodriguez as Southampton’s only recognised strike options for the coming top flight campaign.