Novak Djokovic and Serena Williams have been named ITF World Champions for 2015, after both players won three Grand Slam titles this year.

Djokovic won the Australian Open, Wimbledon and the U.S. Open, amassing a career-best total of 11 titles in 2015 and an 82-6 win-loss record.

Djokovic, who has now won the ITF World Champion title five times, says "my season was the best of my career."

Williams took the Australian Open, the French Open and Wimbledon, holding all four Grand Slam titles before losing in the U.S. Open semifinals. She ended the year with a 53-3 win-loss record.

Williams won the ITF title for the sixth time and says "it has been an amazing year."