King was offered a new deal by Rovers but will instead take his talents to the Premier League with Bournemouth, who have already signed ‘keepers Artur Boruc and Adam Federici this week.
The 23-year-old was in and out of Blackburn’s side this season but made headlines when he scored a hat-trick for them in their 4-1 win over Stoke City in the fifth round of the FA Cup.
Norway-born King has been in England since the age of 16, when he joined Manchester United, but after not making a Premier League appearance for them he joined Blackburn in January 2013.
And he said the chance to play under LMA Manager of the Year Eddie Howe made his decision a slightly easier one.
“The Premier League has always been the dream to play in,” King told Bournemouth’s official website.
“I’ve been on the bench for United, I’ve played in the Champions League and FA Cup but never got on for United in the Premier League.
“So if I do get my chance in the Premier League it will be the first so that played a big factor, but the manager was a bit more important.
“I’ve seen what he’s done with the squad here. I’ve watched a couple of games during the season, and the football Bournemouth play suits me very well I think.
“He loves the style I play and he actually thinks I can fit in with the team that’s done brilliantly in the Championship and hopefully will do well in the Premier League as well.”