Titles, Kings and the Hellenic Constitution

I think that it is POV to mention that calling Constantine a King upsets the Governments. We can't know what upsets them
and it makes no difference anyway. The right way is that calling him a King of Greece, hence giving him a Hellenic title,
means missrespect of the Greek constitution, check also , under which 
there are no titles as are known in other countries (Sir, King, dukes etc). He can be duke of a place in countries that support titles such as the UK and Denmark, but he can't call him self duke of Sparta or duke of Myconos as there is no such thing as duke or King or Sir.