Real announced on Saturday that Casillas was leaving after 16 seasons in the first team to join the Portuguese club and his exit is widely expected to prompt the arrival of the decade-younger David De Gea from Manchester United.
Real published a glowing homage to Casillas on their website (www.realmadrid.com), calling him "the greatest goalkeeper in the history of the club and in the history of Spanish football" and "a symbol of the best in our history".
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However, in an interview with daily El Mundo, Casillas's parents Jose Luis and Mari Carmen said their son, with whom they have a troubled relationship, had been badly treated by Perez since he returned for a second stint as president in 2009.
Casillas had been the victim of an orchestrated campaign of "vilification" in recent years which eventually prompted his decision to quit, they added.
Perez wanted to bring in Juventus and Italy keeper Gianluigi Buffon instead of Casillas as he preferred taller players, El Mundo quoted Mari Carmen as saying.
He was also upset about a financial dispute with Casillas which prompted the player to take legal action against the club in 2009, the parents added.
Real did not immediately respond to a request for comment.

Florentino Pérez e Iker Casillas

Image credit: Imago

"Iker has put up with a great deal, he has suffered psychological pressure and they treated him differently to other players," Mari Carmen told El Mundo.
"I have watched him suffer for many years. It is Florentino who is pushing him out because he wanted to end his career at Real Madrid."
Casillas's mother said former European champions Porto were not prestigious enough for her son, who won three Champions Leagues titles with Real and captained Spain to triumphs at Euro 2008 and Euro 2012 as well as the 2010 World Cup.
"It (Porto) is a third-tier team for someone of Iker's stature," Mari Carmen told the paper.
"A world champion can't end up at Porto. He could have gone wherever he wanted and I wouldn't have cared if it had been Barcelona because they are gentlemen."
Casillas is due to hold a farewell news conference at the Bernabeu stadium later on Sunday.
DID YOU KNOW?
As a child, at about “seven or eight”, Casillas forgot to post his father’s football pools coupon on the very he had correctly predicted all 14 results. The family lost out on an estimated £1m.
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