via a Twitter post on Wednesday, saying that she and Cahill "have decided that it's time to end our working relationship."
Halep won the French Open in 2018, beating Sloane Stephens in the final, and Wimbledon in 2019, defeating Serena Williams in the final.
The Romanian, who turns 30 on Monday, also reached No. 1 in the rankings. She is No. 14 this week.
Halep lost in the fourth round of the U.S. Open this month. She missed the French Open, Wimbledon and the Tokyo Olympics after tearing her left calf at the Italian Open in May.