"It's great to be back at Charlton," Royce told the Charlton website.
"I always got on very well with everyone at the club and when the call came out of the blue a couple of weeks ago, I didn't think twice.
"I'm really looking forward to the new season.
"With Dean Kiely suspended for the first game, that is a great incentive for me, and although he is certainly the number one at the moment, I'll be looking to have a good pre-season and put him under some pressure."