This evening, after having drunk the health of King Michael I on his ninetieth birthday, it occurred to me that he is noteworthy for the his longevity as a monarch. King from 1927 until 1930 and since 1940, allbeit forced into exile in 1947 with an enforced abdication which he subsequently disclaimed and which was exacted under pressure, and not therefore voluntary, and only returning to the country in recent years in anambiguous position, he has been a monarch longer, at 74 years already, than those better known long-reigning rulers, Queen Victoria (63 and a half years), Emperor Francis Joseph (just short of 68 years) and King Louis XIV (72 years).
In fact the only person I can think to have potentially exceeded that is Otto of Austria, who as the de jure Emperor Otto I of Austria and King Otto II of Hungary may be assigned a reign from his father's death in 1922 until his death earlier this year of 89 years. His various renunciations of claim may be discounted as what he considered necessary at the time, and may be therefore discounted had been able to exercise his hereditary rights.
If however one looks at monarchs who did actually occupy their thrones, then King Michael is the longest reigning European monarch - the tragedy for him and his people is that he has not been enabled to exercise that role.
The Romanian Royal Standard,
as adopted in 1922