In August 1558, Charles was taken seriously ill with what was later revealed to be malaria. He died in the early hours of the morning on 21 September 1558, at the age of 58, holding in his hand the cross that his wife Isabella had been holding when she died.  Charles was originally buried in the chapel of the Monastery of Yuste, but he left a codicil in his last will and testament asking for the establishment of a new religious foundation in which he would be reburied with Isabella. Following his return to Spain in 1559, their son Philip undertook the task of fulfilling his father's wish when he founded the Monastery of San Lorenzo de El Escorial. After the Monastery's Royal Crypt was completed in 1574, the bodies of Charles and Isabella were relocated and re-interred into a small vault directly underneath the altar of the famous Basilica of the Monastery, in accordance with Charles's wishes to be buried "half-body under the altar and half-body under the priest's feet" side by side with Isabella. They remained in this vault until 1654 when they were later moved into the Royal Pantheon of Kings by their great-grandson Philip IV, who, in doing so, disrespected his great-grandfather's wishes.  On one side of the Basilica are bronze effigies of Charles and Isabella, with effigies of their daughter Maria of Austria and Charles's sisters Eleanor of Austria and Maria of Hungary behind them. Exactly adjacent to them on the opposite side of the Basilica are effigies of their son Philip with three of his wives and their ill-fated grandson Carlos, Prince of Asturias.

Answer this question "Who ruled after him?" by extracting the answer from the text above.
Following his return to Spain in 1559, their son Philip undertook the task of fulfilling his father's wish when he founded the Monastery of San Lorenzo de El Escorial.