Former world number one Ana Ivanovic today announced her retirement from tennis. The 29-year-old Serbian held the top spot for 12 weeks in 2008, the season when she claimed her sole Grand Slam success by winning the French Open. The Serb made the announcement via Facebook tonight. After her disappointing fifth-round exit from last August's US Open, Ivanovic revealed that she would be ending her season early to fully recover from a series of injuries that have hindered her in recent years. Although she insisted at the time she would be returning to the sport, Ivanovic has now decided to bring her career to a close.