Iker Casillas has admitted that Jose Mourinho's off-field antics including poking former Barcelona boss Tito Vilanova in the eye was a key factor behind their high-profile fallout at Real Madrid.
During their time together at the Spanish giants, Casillas and Mourinho endured a difficult relationship, with the long-serving shot-stopper being dropped in favour of Diego Lopez, before the Portuguese was too ousted in 2013.
Mourinho's most shameful incident at the Santiago Bernabeu arguably came when he gouged the eye of Vilanova - at the time Pep Guardiola's assistant at the Catalan giants - after a reckless challenge by Marcelo on Cesc Fabregas sparked a scuffle between the sides in a Supercopa tie in August 2011.
Marcelo was sent off as a result in Barcelona's 3-2 win and Mourinho was initially banned for two matches, while Vilanova was handed a one-match ban for a retaliatory slap before both coaches saw their suspensions overturned.
But speaking in Colgar las Alas, a documentary on Spainsh station Movistar+, Casillas admitted it was that sort of behaviour - which he insisted only 'tacky clubs' resort to - that led to their relationship deteriorating following a players' strike in the same month as the incident.
'As the captain, I spoke to my team-mates and we decided that we weren't going to play which meant the opening games of the season wouldn't go ahead,' Casillas said.
'We said a couple of things that neither of us liked and took badly but it was left there. Then came the Super Cup.
'We gave a terrible impression. There were scraps, battles, giving your heart and soul… but the other things (poking Vilanova's eye) - that was the kind of thing you might see at other clubs - tacky clubs, who need to resort to that sort of thing, and that is not for us.
'We played Levante, a game in which we fell further behind to Barcelona. That was the moment when we stopped talking. We were alone together in a room and he starts telling me that I should be more open and honest.
'I told him that I didn't think it was right for a professional to poke another coach in the eye. Someone from the press department at the club grabbed us and told us to calm down, to talk it through. We sat down again and said what we had to say face to face.'
World Cup winning goalkeeper Casillas also admitted his issues with Mourinho resurfaced in Mourinho's last campaign at the club, and described the previous two years as a 'love-hate relationship' between the duo.
'There were two or three games [in 2012-13] in which we didn't play well,' the 39-year-old added.
'That was when the old resentment resurfaced, when we fell behind in the table. Our relationship deteriorated. It had reached the point of no return by the third year.
'Up until the second year it was a love-hate relationship. He told me he didn't think I was focused, he didn't think I was playing well… I thought that maybe it was true. I had other things on my mind that I was worried about at the time.'
The news comes a couple of months after Casillas - who left the Spanish capital for Porto in 2015 before announcing his retirement in August this year - revealed that Mourinho was one of the first people to call him after he suffered a heart attack last year.
Casillas was rushed to hospital in May 2019 after he suffered a heart attack at Porto's training ground, and the three-time Champions League winning goalkeeper spent five days in hospital.
'A lot of people don't know it but Jose Mourinho was one of the first people to call about me, to call me to find out how I was,' Casillas told ESPN.
The Spaniard was subsequently seen hugging Mourinho at a FIFA congress and admitted that the event was an emotional occasion for him.
He said: 'I saw people I had not seen for a long time, it makes you appreciate the little things in life,' he said. 'You live more from day to day, you stop just being in your own little world.
'I was very lucky, other people don't have that.
'I felt that I was definitely going to die that day, and the circumstances forced me to reconsider everything. I'm a privileged person. If I can continue to play football, I will do that.'