VIDEO : Daniel Radcliffe Shares Heartfelt Tribute to Alan Rickman

The news of Alan Rickman's passing on Thursday provoked an instant outpouring of emotion from across the entertainment world. But amid the tweets from co-stars and colleagues from both stage and screen, one of the most heartfelt tributes has come from the lead star of arguably Rickman's most famous films. On his Google Plus page, Daniel Radcliffe wrote that Rickman was "undoubtedly one of the greatest actors" that he had ever worked with. "He is also one of the loyalest and most supportive people I've ever met in the film industry," he added, claiming that Rickman was encouraging long after Harry Potter had finished.