It has been claimed that several members of Vicente Del Bosque's side do not see eye to eye, but while the goalkeeper insists that is not true, he concedes it was only a year ago.
"If the Euros had been in 2011, it [the Clasico rivalry] would have been a problem, but now we have a laugh about it," the Madrid goalkeeper is quoted as saying by Marca.
"This tension is now gone and I think we should look on the bright side: we have moved on."
Spain go into Euro 2012 as the reigning world and European champions, but Casillas acknowledges that history counts for nothing when it comes to major international tournaments.
"We know that the past is worthless," he explained. "We have a good record but we cannot survive on our memories. We want to do well and continue winning."
Spain kick off their campaign against Italy, who are being written off by many pundits after their shocking 3-0 defeat by Russia in their final warm-up fixture.
Nonetheless, Casillas remains very wary of the threat posed by the Azzurri.
"I've seen videos of Italy and I think they a great team," the Blancos shot-stopper declared. "They have many interesting players and they have been renovated.
"They have both veterans and hopeful youngsters, with a lot of players from Juventus. I have maximum respect for them."
Spain's opening Group C clash with Italy gets under way at 18:00CET on Sunday.