The worst King in modern time was probably King Constantine of the Hellenes. His extremely poor handling of the coup d'état by the military junta in 1967 (first he reluctantly accepted the establishment of the military junta then he headed a hopelessly failed contra-coup d'état and was forced into exile). The establishment of the military junta was possibly a result of the political unstability and unrest in Greece caused by the King's openly opposition of the democratically elected Government of Georgios Papandreou.
When even the military, usually a cornerstone of a monarchy, oppose against the King, then there is seriously something wrong with the way the King assessed and handled the political situation of Greece. It is no wonder, that even in the most hefty turmoils of last years, the total failure of Greek politics, the bankruptcy of Greece which caused an immense downfall of welfare, that even then there was no single call for a restoration of the monarchy, no any longing "back to great times". This is quite telling. My nomination for "worst monarch" in modern times (and in Europe) goes to Constantine II.
There's a lot that I don't know about the circumstances surrounding the 1967 coup in Greece but this seems to me to be rather a harsh judgement of Constantine II.
From what I understand, the context of the military coup is extremely complex. The legacy of division from the Civil War which had occured twenty years earlier, the strategic importance of Greece at the height of the Cold War to the Americans/the West, the privileged position of the Greek military in relation to government and society and the long-standing and bitter dynastic/tribal rivalries of the leading Greek political families, amongst other considerations, meant that the country was fragile, vulnerable and divided.
King Constantine's situation, particularly as the institution of the monarchy itself was hardly secure, is thus not to be envied.
Added to this, his father's early death and his young age on ascending the throne meant that his "training" was incomplete; he had been in the job for barely three years and was still only a 26-year-old when the crisis erupted, thus being short of experience and "authority"; and he had a 20-year-old wife and two infant children to protect.
With hindsight, we can criticise the King's actions before, during and after the coup and find his judgement wanting in comparison to King Juan Carlos, a 43-year-old who was well-established on the throne at the time of the attempted coup in 1981. However, I remain to be convinced that his motivations for the decisions he took were anything other than honourable.
I think that the principal reason that there haven't been any serious calls for a restoration of the monarchy since is that Constantine has been a very convenient scapegoat for ALL sides. As long as the blame/ridicule is directed at him, it is possible to overlook the facts that the Greek military betrayed the democratic state to protect its own interests, that the political dynasties of both right and left have put power and self-interest ahead of good governance and, dare I say it, that the Greek people have allowed all this to happen.
Moreover, is what Constantine did (or didn't do) in Greece 1967
worse than the records of Vittorio Emanuele III in Italy when faced with Mussolini, of Alfonso XIII, Nicholas II, Wilhelm II or of Carol II?