HRH Infanta Maria Adelaide, aunt of Portugal's rightful king the Duke of Braganza, who recently celebrated her 100th birthday, has died in Lisbon. I am glad she reached (and apparently was able to enjoy) this milestone, though sorry that she had to spend her entire long life as a member of a non-reigning royal family, the Portuguese monarchy having fallen slightly over a year before she was born in January 1912. Maria Adelaide was the first and so far only centenarian of royal birth in European history. (Only royals-by-marriage Princess Alice Duchess of Gloucester and Queen Elizabeth the Queen Mother have lived longer.) Incredibly, due to late marriages by her father and grandfather, she was only two generations removed from the controversial de facto king (1828-34) Dom Miguel (1802-1866), uncle and rival of Maria II. The infanta's passing is also particularly notable in that she was the last surviving member of any European royal family who had been born before the First World War, severing a last link to the "Belle Époque" era of European royalty. Requiescat in pace.
I believe there are now three possible contenders for "oldest living European royal" depending on exactly how "royal" is defined. The oldest living member of a European royal family by marriage is Princess Lilian [Davies], Duchess of Halland (b 30 Aug 1915), widow of Prince Bertil of Sweden (whose long-delayed 1976 marriage unlike those of his brothers was fully accepted by the court). The oldest living person born into any "Section I" (reigned since the Napoleonic era) Gotha family is Princess Elisabeth [of Lippe] (b 23 Jan 1916), widow of Ernst August Prince of Solms-Bruaunfels. The oldest living person born into the reigning family of a European kingdom is the former Prince Carl Johan of Sweden, Count Bernadotte of Visborg (b 31 Oct 1916).