Ferdinand I of Romania Ferdinand I ( 24 August 1865 – 20 July 1927 ) was King of the Romanians from 10 October 1914 until his death in 1927 . Early life . Born in Sigmaringen in southwestern Germany , the Roman Catholic Prince Ferdinand Viktor Albert Meinrad of Hohenzollern - Sigmaringen . The name was later shortened simply to Hohenzollern . Within his family , he was called " Nando " . Ferdinand I was the son of Leopold , Prince of Hohenzollern - Sigmaringen and Infanta Antónia of Portugal ( 1845 – 1913 ) , daughter of Queen Maria II and King Ferdinand II , a Prince of Saxe - Coburg and Gotha and heir to the Slovakian originated Hungarian magnates of Kohary on his mother ' s side . Following the renunciations , first of his father in 1880 and then of his elder brother Prince Wilhelm of Hohenzollern - Sigmaringen in 1886 , young Ferdinand became the heir - presumptive to the throne of his childless uncle , King Carol I of Romania , who would reign until his death in October 1914 . In 1889 , the Romanian parliament recognized Ferdinand as a prince of Romania . The Romanian government did not require his conversion to Eastern Orthodoxy from Catholicism , as was the common practice prior to this date , thus allowing him to continue with his born creed , but it was required that his children be raised Orthodox , then the state religion of Romania . For agreeing to this , Ferdinand was excommunicated from the Catholic Church , although this was later lifted . Ferdinand ' s mother ' s first cousin Tsar Ferdinand I of Bulgaria sat on the throne of the neighbouring Bulgaria beginning in 1887 and was to become the greatest opponent of the kingdom of his Romanian cousins . The neighboring Emperor Francis Joseph , monarch of Austria - Hungary and as such , ruler of Transylvania , was Ferdinand ' s grandmother ' s first cousin . Ferdinand , a complete stranger in his new home , started to get close to one of Queen Elisabeth ' s ladies in waiting , Elena Văcărescu . Elisabeth , very close to Elena herself , encouraged the romance , although she was perfectly aware of the fact that a marriage between the two was forbidden by the Romanian constitution ( according to the 1866 Constitution of Romania , the heir - presumptive to the throne was not allowed to marry a Romanian ) . The affair caused a sort of dynastic crisis , in 1891 . The result of this was the exile of both Elisabeth ( in Neuwied ) and Elena ( in Paris ) , as well as a trip by Ferdinand through Europe in search of a suitable bride , whom he eventually found in Queen Victoria ' s granddaughter , Princess Marie of Edinburgh . Marriage . In Sigmaringen on 10 January 1893 , Prince Ferdinand of Romania married his distant cousin , the Lutheran Princess Marie of Edinburgh , daughter of Anglican Prince Alfred , Duke of Edinburgh and the Orthodox Grand Duchess Marie Alexandrovna of Russia . Marie and Ferdinand were third cousins in descent from Franz Frederick Anton , Duke of Saxe - Coburg - Saalfeld . Marie ' s paternal grandparents were Victoria of the United Kingdom and Prince Albert of Saxe - Coburg - Gotha . Her maternal grandparents were Alexander II of Russia and Marie of Hesse and by Rhine . The reigning Emperor of the neighbouring Russia , at the time of the marriage was Marie ' s uncle , Tsar Alexander III , who would be succeeded by his eldest son , Marie ' s cousin , Tsar Nicholas II , the following year . The marriage produced 3 sons : Carol , Nicholas and Mircea ( one of whom , Mircea , died in infancy ) and 3 daughters : Elisabeta , Maria ( Mignon ) and Ileana . The marriage was unhappy and the couple ' s two youngest children , Ileana and Mircea , are generally acknowledged to have been sired by Marie ' s long - time lover , Barbu Ştirbey . King of the Romanians . Ferdinand succeeded his uncle on the latter ' s death ( Carol I died without surviving issue ) as King of Romania on 10 October 1914 , reigning until his own death on 20 July 1927 . He was the 1 , 174th Knight of the Order of the Golden Fleece in Austria in 1909 and the 868th Knight of the Order of the Garter in 1924 . World War I . Though a member of a cadet branch of Germany ' s ruling Hohenzollern imperial family , Ferdinand presided over his country ' s entry into World War I on the side of the Triple Entente powers against the Central Powers on 27 August 1916 . Thus he gained the nickname " the Loyal " , respecting his oath when sworn in before the Romanian Parliament in 1914 : As a consequence of this " betrayal " toward his German roots , Kaiser Wilhelm II had his name erased from the Hohenzollern House register . Despite the setbacks after the entry into war , when Dobruja and Wallachia were occupied by the Central Powers , Romania fought in 1917 and stopped the German advance into Moldavia . When the Bolsheviks sued for peace in 1918 , Romania was surrounded by the Central Powers and forced to conclude the Treaty of Bucharest , 1918 . However , Ferdinand refused to sign the treaty . When the Allied forces advanced on the Thessaloniki front , they knocked Bulgaria out of the war , and Ferdinand ordered the re - mobilization of the Romanian Army . Romania re - entered the war on the side of the Triple Entente . The outcome of Romania ' s war effort was the union of Bessarabia , Bukovina and Transylvania with the Kingdom of Romania in 1918 . Ferdinand became the ruler of a greatly enlarged Romanian state in 1918 – 1920 following the Entent ' s victory over the Central Powers , a war between the Kingdom of Romania and the Hungarian Soviet Republic , and the civil war in Russia , and was crowned King of Romania in a spectacular ceremony on 15 October 1922 at the historic princely seat of Alba Iulia , in Transylvania . A new period of Romanian history began on the day of the Union of Transylvania with Romania ( Great Union Day , " Marea Unire " ) . This period would eventually come to an end with the international treaties that led up to World War II . These ceded parts of Romania to its neighbors . As such , they are widely seen as an attempt to provoke the country into taking sides and joining the war . After the war . Domestic political life during his reign was dominated by the conservative National Liberal party led by the brothers Ion and Vintilă Brătianu . The acquisition of Transylvania ironically enlarged the electoral base of the opposition , whose principal parties united in January 1925 – October 1926 to form the National Peasant Party . Ferdinand died in Sinaia in 1927 , and was succeeded by his grandson Michael I , under a regency . The regency had three members , one of whom was Ferdinand ' s second son , Prince Nicholas .