Tuesday 22 December 2015 16:15, UK
Novak Djokovic and Serena Williams have retained their titles as world tennis champions in the men's and women's singles respectively.
For Djokovic, it was his fifth triumph in a row, while Williams has been crowned for a fourth straight year - and sixth time in all.
During another momentous season, both players lifted three of the four Grand Slam titles.
Serb Djokovic won in Melbourne, London and New York, while losing to Stan Wawrinka in the French Open final.
American Williams won the first three women's slams before suffering a shock US Open semi-final defeat to the-then world No 43, Roberta Vinci of Italy.
Djokovic collected 11 ATP Tour singles titles in all and ended 2015 with a win-loss record of 82-6.
Williams, meanwhile, had arrived at the US Open in late August having completed a second 'Serena Slam' - four majors in a row - and another triumph at Flushing Meadows would have given her a first calendar slam.
Williams, who also suffered just six defeats while collecting five titles, said: "It means a lot to me to be named the ITF world champion for the sixth time.
"I am proud to have achieved my second Serena Slam, in what has been an amazing year for me. Thank you for this recognition and for the undying support of the tennis community."
Williams has not played a competitive match since losing to Vinci who was beaten by Flavia Pennetta in the final in New York.
The ITF has been awarding world titles since 1978 with Williams (6), Martina Navratilova (6) and Steffi Graf (7) the most successful in the women's game.
Pete Sampras, with six successes, has won the men's title most times, followed by Djokovic and Roger Federer with five each.
Martina Hingis of Switzerland and India's Sania Mirza were named women's doubles world champions, with Jean-Julien Rojer of the Netherlands and Romania's Horia Tecau taking the men's award.
