(CNN) Novak Djokovic broke down in tears while reflecting on his friendship with Kobe Bryant at the Australian Open.

Speaking after his quarterfinal victory over Milos Raonic, Djokovic hailed Bryant, who died alongside his daughter and seven others in a helicopter crash Sunday , as "one of the greatest athletes of all time".

"He inspired myself and many other people around the world," the Serb said in Melbourne.

"I had the fortune to have a personal relationship with him over the last 10 years.

"When I needed some advice and some support he was there for me. He was my mentor, my friend. It's heartbreaking to see and hear what has happened to him and his daughter."

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