Signed initially on loan in November 2012, impressive displays meant that Rovers moved quickly to make the deal a permanent one with the opening of the January 2013 transfer window.
The Norwegian international has put pen-to-paper on a two-and-a-half year deal with the option of a further year.
Oslo-born, Josh started his footballing career with Valerenga before being scouted by Manchester United, signing for the Premier League club in January 2008 as a 16-year-old.
King quickly progressed through United's Academy and then onto their Reserve-team before securing a loan move to Preston North End in 2010.
The following year was spent earning experience with Bundesliga side Borussia Moenchengladbach, whilst last year the striker was on loan at Hull City.
Able to play through the middle or out wide, King has honours for Norway at all levels with four caps for the senior squad, scoring one goal.