Tottenham manager Mourinho fell out with Casillas when they were together at Real as he benched the captain and goalkeeper in favour of Antonio Adan. The clash sparked Casillas' slide at Real as he struggled to re-establish himself as the club's outright No1, even after Mourinho's departure.
Casillas would eventually depart for Porto three years later in 2015.
Casillas recalled, speaking to the Fundación TELMEX TELCEL via O Jogo: "We were two people who got along for a year and a half, but the following year we had discrepancies, which were normal between the captain and the coach. It does not mean that it is more than the coach, but the captain has to speak practically every few days with him and the relationship wears out.
"José Mourinho thought that I was not at the level of another teammate or, adding to that, that our relationship was not so good and that it was much easier for him to choose between one or the other. It was a more personal matter."
Casillas was asked why he didn't push back at the time against Mourinho, but the now retired goalkeeper says he wanted to put the club first.
He explained, "I decided not to have such a relationship with him, because I didn't like the things I saw and he chose another teammate. This last situation reached me when I was more mature, at the age of 33. You look at the club, you try not to create more controversy than there was already and, well, I would do what I did at that time and I think I was not wrong."
Concluding, Casillas insists he and Mourinho have since repaired their relationship, with neither man bearing a grudge. The pair won the LaLiga together in 2012, stopping Pep Guardiola's Barcelona at the time.
The Spaniard revealed: "There are many things that people do not see, but I have a good relationship with him (today). We have met several times since then and we have had beautiful words. It is not a question of continuing to hold a grudge, everyone was looking for the best for the team."
In 17 years with Real Madrid, Casillas won five LaLiga titles, three Champions League trophies and three Club World Cups.
- updated September 28