Which surname did Constantine II, the former King of Greece, adopt to get his Greek passport?

Constantine II (born 2 June 1940) is the former King of Greece. He reigned from 6 March 1964 until the abolition of the monarchy on 1 June 1973.

Until 1994, Constantine's official Greek passport identified him as "Constantine, former King of the Hellenes". A law passed in 1994 stripped him of his Greek citizenship, passport, and property. The law stated that Constantine could not be granted a Greek passport unless he adopted a surname.

Constantine has stated: "I don't have a name—my family doesn't have a name. The law that Mr. Papandreou passed basically says that he considers that I am not Greek and that my family was Greek only so long as we were exercising the responsibilities of sovereign, and I had to go out and acquire a name. The problem is that my family originates from Denmark, and the Danish royal family haven't got a surname." Glücksburg, he said, was not a family name but the name of a town. "I might as well call myself Mr. Kensington.

Constantine freely travels in and out of Greece on a Danish 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, and Constantine is a Prince of Denmark in his own right.