Complex sentence: He freely travels in and out of Greece on a Danish diplomatic passport, as "Constantino de Grecia" (Spanish for "Constantine of Greece"), because Denmark (upon request) issues diplomatic passports to any descendants of King Christian IX and Queen Louise.
Split into simpler sentences: He freely travels in and out of Greece on a Danish diplomatic passport, as "Constantino de Grecia" (Spanish for "Constantine of Greece"). This, because Denmark (upon request) issues diplomatic passports to any descendants of King Christian IX and Queen Louise.