Novak Djokovic broke down on Tuesday as he paid tribute to late basketball star Kobe Bryant, describing him as a “mentor” and a “friend” for the past 10 years.

Djokovic, speaking after his Australian Open quarter final win against Milos Raonic, said it was “heartbreaking” to hear about Bryant, who died in a helicopter crash on Sunday along with his daughter and seven others.

“He was one of the greatest athletes of all time, he inspired myself and many other people around the world,” Djokovic said in an on-court interview at Rod Laver Arena, wearing a tracksuit with the initials KB.

“I had the fortune to have a personal relationship with him over the past 10 years. When I needed some advice and some support, he was there for me. He was my mentor, my friend and it’s just heartbreaking to see and to

hear what has happened to him and his daughter,” Djokovic said, before breaking off to compose himself.

Djokovic and many other legends of tennis, including Billie Jean King and Martina Navratilova, have voiced their grief over the death of the former LA Lakers shooting guard, regarded as one of the greatest basketball players.

On Monday night, NBA superstar LeBron James posted a tribute to Bryant and his daughter Gianna on Instagram, saying he was “heartbroken and devastated.” He referred to Bryant as his brother.

“Man I sitting here trying to write something for this post but every time I try I begin crying again just thinking about you, niece Gigi and the friendship/bond/brotherhood we had!” James wrote. “I literally just heard your voice Sunday morning before I left Philly to head back to LA. Didn’t think for one bit in a million years that would be the last conversation we’d have.”

On Sunday, footage emerged of James and other Lakers teammates coming off the team plane and embracing one another. Bryant’s death came the day after James passed him on the NBA’s all-time scoring list.

Separated in age by just six years, the men were friends and regarded as the heirs to Michael Jordan. Their ties had been nurtured over close to two decades, ever since the day in 2002 when Bryant and James met in Philadelphia. The next yearJames entered the draft.

They eventually played alongside each other in the Olympics and were fierce rivals when they played for opposing teams in the NBA.