Toni Nadal, the uncle and former coach of 20-time Grand Slam champion Rafael Nadal, has joined the coaching team of Canadian Felix Auger-Aliassime.
Nadal, widely known as 'Uncle Toni', coached his nephew from childhood and through his adult career until he stood down in 2017.
He will now join the team of highly-rated Auger-Aliassime, 20, starting at next week's Monte Carlo Masters.
"I never considered before to work for someone else," Nadal, 60, said.
Nadal left his nephew's team after helping him to his first 16 Grand Slam titles to work exclusively at the Rafael Nadal Academy in Majorca.
Auger-Aliassime is ranked 22nd in the world and will also keep his current coach Frederic Fontang.
"I sat down with Fred and my team and parents and I thought to myself it would be good to go to someone who has been at the highest level of our sport, who has been to where I want to go," said the Canadian, who is yet to reach a Grand Slam quarter-final.
Nadal said he would not be in either player's box if Auger-Aliassime and his nephew met in the coming months.
"If [Rafa] has to lose to someone then I would rather him lose to Felix," he said. "I'm still his uncle and have many years of involvement with him."
Meanwhile, British number one Dan Evans failed to convert four match points in defeat by Lorenzo Musetti at the Sardegna Open in Italy.
Evans led 6-3 in the deciding set tie-break but the Italian, the youngest player in the world's top 100, fought back to win 6-1 1-6 7-6 (10-8).
Evans was the top seed for the clay-court event in Cagliari.