Lopez spent seven years at Valdebebas as a youth player and after spells at Villarreal and Sevilla has now returned to Real Madrid six years after leaving.
The 31-year-old shot-stopper, signed following the news that Iker Casillas is set to be out injured for the next two months, is delighted to be returning to the club he considers "home".
"It is a dream to return home," he told EFE.
"Today the deal has happened very fast and I am very happy to return to the place I consider my home.
"For a Madridista like myself, to return to Real Madrid is the best thing that could have happened in my career. I am eager to [start] this great new challenge."