Novak Djokovic has appointed Andy Murray to coach him into and through the Australian Open.
Announcing the collaboration, Djokovic said: "I am excited to have one of my greatest rivals on the same side of the net, as my coach."
He said he was looking forward to the start of the season and competing in Australia alongside Murray, with whom he said he has "shared many exceptional moments on the Australian soil".
In a video posted on X, the Serbian player added: "We had some of the most epic battles in our sport... I thought our story was over, turns out it has one final chapter.
"It is time for one of my toughest opponents to step into my corner."
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Three-time Grand Slam winner Murray retired in August after exiting the men's doubles at the Paris 2024 Olympics.
The announcement means he will join forces with the man who was his biggest nemesis during his professional playing career, with Murray losing four Australian Open finals to Djokovic in 2011, 2013, 2015 and 2016.
But Murray claimed victory over Djokovic at the US Open in 2012 and Wimbledon in 2013.
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In a statement, Murray added: "I'm going to be joining Novak's team in the off-season, helping him to prepare for the Australian Open.
"I'm really excited for it and looking forward to spending time on the same side of the net as Novak for a change, helping him to achieve his goals."
Djokovic is a 24-time Grand Slam champion who has spent more weeks at number one than any other player in tennis history.
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The Serbian player split with coach Goran Ivanisevic earlier this year.
He said he hopes adding Murray to his team will help him secure a record 11th Australian Open win.
Djokovic has slipped to seventh in the world rankings, having gone through a calendar year without winning a Grand Slam for the first time since 2017.
The Australian Open runs from 12 to 26 January.