Ancelotti took over at the Parc des Princes in December 2011, guiding the club to their first Ligue 1 title since 1994 last season, as well as the quarter-finals of the UEFA Champions League.
But despite that success, Ancelotti chose to leave the French capital in the close-season, citing a change in philosophy at PSG as the reason behind his switch.
"When I signed with PSG I believed in a project. New players were joining, a team was about to be built and this is something that takes time," Ancelotti told L'Equipe.
"The first six months were good but the following year I understood that the management had changed their point of view. There was no project anymore... just an idea to get results immediately."
Ancelotti had been under some pressure in the second half of last season following a poor run of form in December, but a 1-0 defeat to Reims in March proved to be the tipping point for the 54-year-old.
"It is true that we had payed badly (at Reims). But I thought that after the good three months we just had, I would have a bit of tranquility," he added.
"The day after (the loss), I told (then sporting director) Leonardo that I would not coach (PSG) at the end of the season.
"Everybody thought that I left because I had Real Madrid. This is not true. I made this decision, I don't know if it's the right one, but it had become too complicated at PSG."
The Italian, who is so far unbeaten as Real boss, was also quick to criticise midfielder Mesut Ozil - who left to join Arsenal on the final day of the transfer window - for his unwillingness to fight for his place with the club.
"At great clubs there are two ways to react to competition: either you stay to fight for your position or you leave," he added.
"Ozil preferred to leave. He said he left the club because he didn't feel trust. But he never came to talk to me."
