Saints and Charles meet City in the FA Cup semifinal later on Saturday.
City fan and former academy player Charles told The Sun: “I started training with the first team at 17 and as a fan was looking at players I idolised.
"For a couple of years, you’re trying to get up to their level and learn from them.
“There’s nowhere better in the world to grow up as a footballer — the way I play is the way City taught me.
“And now I want to use all of that to make my own mark against City. Although they present a huge challenge, who knows what can happen.”
Charles added: “Fernandinho was my favourite player growing up.
“So to train with him before he left was a great experience and, of course, Rodri too.
“I’d be watching them, learning, asking questions. It was all about the reading of the game, game intelligence and having a good range of passing.”