Addicks Head of Recruitment Steve Gallen, speaking to Charlton's website, said: "We actually tried to get him in the summer.
"We've tracked him all the way through since, watching U23 games. At times he's played as a midfielder, at times he's played as a 10, he's played as an 11, he's played as a nine.
"He's scored goals in a couple of games. He's scored a couple of hat-tricks. We know exactly what we're getting and we're really, really pleased to get him."