The most surprising part is the timing. Murray only retired from playing four months ago. That time has been shared between his family and his golf clubs, but as he told the Control the Controllables podcast last year, if his children are at school, he is often bored by Wednesday lunchtime.

The opportunity to work with Djokovic is unlikely to come around again and, having lost four Melbourne finals to the Serb, he may think he will never have a better chance to win the Australian Open.

Joking aside, there do not appear to be many downsides. Djokovic has not currently entered any events before the Australian Open, so Murray should be free to enjoy the Christmas holiday at home after some work together during the off-season.

Their Melbourne practice sessions will be box office, and it will be enthralling to see how their relationship develops and whether Murray could be a feature of Djokovic's team at some of the year's other Grand Slams.

"They always got on well, but I don't think it would have been as close as it maybe was when they were younger - or it would be now," Delgado says of their relationship.

"There was just so much on the line. But they had immense respect for each other.

"Andy always spoke so highly of his [Djokovic's] game and how difficult it was to play against him. The respect was sky high."

The final great act in their playing rivalry was the race to be the year-end world number one in 2016.

"When me and Novak speak with each other, we don't talk about tennis, rankings, the matches we play against each other," Murray said earlier that year.

"Maybe when we finish playing, that might change."