It's well documented that Jose Mourinho fell out with Real Madrid legend Iker Casillas during his three-year managerial stint in the Spanish capital.
The 36-year-old goalkeeper is currently winding down his career at Porto.
"At the beginning there was a lot of connection, we interacted a lot, but in the end, there wasn't a very good feeling," said Casillas on his relationship with Mourinho.
"It's like a couple, at the beginning you are very much in love and then it is no longer enough."
Some more light has been shed on their awful relationship by 38-year-old Flamengo goalkeeper Julio Cesar.
The Brazilian stopper played under Mourinho at Inter Milan and has given an insight into how terribly the Manchester United manager treats his players.
It's something Luke Shaw will surely be able to relate to.
Mourinho bullied Julio Cesar
"The first year was great [under Mourinho], but the second one was more difficult," said Cesar on the Selecao Sportv programme, as per Marca. "I went into games with a fear of being wrong, and I thought: either I face it or it ends my career.
"In training Mourinho approached me and said 'you are the best goalkeeper in the world, but today you're a Serie C goalkeeper.'
"There was a time when Mourinho wanted me to play with a yellow shirt," Cesar said. "But it wasn't part of the colours of the goalkeepers of that season, which were white, black and grey.
"He gave me a yellow shirt, which was the training shirt, and I told him I was not going to play in yellow.
"Mourinho mocked me in every way possible and told me I was afraid of the ball.
"In short... I played in yellow."
Savage text about Casillas
Brazil beat Spain 3-0 in the 2013 Confederations Cup final and Cesar was chosen as the best goalkeeper of the tournament.
The former Inter Milan stopper collected his award wearing a 'Casillas' top as a tribute to the legendary Spanish 'keeper.
"When I got to the dressing room, I saw a message from Mourinho on my cell phone," said Cesar.
"'You're crazy, it's Casillas who would have to put on your shirt and not you,' it read.
"And he told me that with only one arm I stopped more than Casillas."
That is just savage - and incredibly unprofessional.
Casillas reportedly went to the Brazilian dressing room after the final to thank Cesar for the touching gesture.
"Iker went to the dressing room to talk to me and I told him to have a discussion with Mourinho, which is difficult but he had to face it," Cesar continued.
"Mourinho likes to go face to face with the players who are considered stars in the teams that he coaches."
The 55-year-old Man United coach is quite clearly a bully.