The Inception star heaped praise on the prince before presenting a prize onstage at the Prince's Trust Celebrate Success Awards, which recognise youngsters who have overcome difficulties.
Hardy told reporters on the red carpet, "I got involved with the Prince's Trust because I believe what they do is fantastic.
"I wanted to give back in any way that I could to my community and Great Britain, and I was looking for something to get involved with.
"The Prince's Trust is about helping young people up the line and helping (them) out of situations where they're struggling, and putting them in a place where they're in a much better position to deal with what life throws at them and turn their lives right around. I thought that was something that I'd like to be a part of, and just asked if I could help out in any way."
Later in the evening, Hardy shook hands with Prince Charles and they chatted about their charity work.
Former Spice Girl Emma Bunton, an ambassador for the trust, also attended the event, as did British actress Keeley Hawes and singer Emeli Sande.