Stewart has joined the Addicks until January.
Powell told the South London Press: "Cameron is someone who came to my attention way back. I always thought he was a good player and he had a superb season at Hull when he first went there. He is a quick, direct winger. We'll need to bring him up to speed because he had a minor injury through pre-season.
"He has come in short term but I'll be keeping my eye on him as someone that could be here longer. Most players are going away this weekend but Cameron is staying in London and wants to do extra sessions. That shows his attitude - he wants to shine and hopefully we can give him a platform to do that."
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