Boris Becker says he was surprised by the level of criticism when world number one Novak Djokovic took him on as his coach last year.
The former Wimbledon champion had been seen on television as a commentator but many felt Becker, whose off-court escapades threatened to eclipse his tennis achievements, did not have much to offer the Serbian 15 years after his retirement.
But Djokovic's victory at Wimbledon in July, in a classic five-setter against Roger Federer, showed the value of input from one of the game's greatest serve-volleyers.
"It was a little bit strange, (I was) a little bit surprised," Becker told CNN's Open Court when asked about the reaction to his appointment. "I wasn't aware I had that many doubters.
"This is a part of sometimes being Boris Becker, being so much in the front row of life, that a lot of people feel like they are entitled to their opinion even though they have no idea about me."
The German said he was honored when approached by Djokovic in October, but he has had to be tough.
"He's a great student. Yet he is very hard-headed. He is very convinced about his way. He should be - so some of the conversations weren't that easy," the 46-year-old added.
Becker, the winner of six grand slam titles including three at the All England Club, said this year's final was a "nightmare' after Federer came back to win the fourth set after saving a match point.
"I was a little bit worried to say the least, I thought Novak was on the ropes - Roger did another Roger." But Djokovic held on to win the fifth set and his seventh major title.
"It felt like I came around full circle. I truly love Wimbledon, it's given me everything that I am today," he said. "And it felt right to be coaching Djokovic and it felt right for him to win."
Djokovic will begin his pursuit of a second U.S. Open title against Argentine Diego Schwartzman when the season's final grand slam begins next week.
(Writing By Robert Woodward, editing by Pritha Sarkar)