In the 1990s, Fife's mitochondrial DNA (mDNA) was used to help identify bones recovered in Siberia in 1979 as the remains of Tsar Nicholas II of Russia, who was executed in 1918 along with his wife and children. Queen Alexandra, the Duke of Fife's maternal great-grandmother, was the older sister of Nicholas II's mother, Dagmar. The test required a female line descendant, as mDNA is passed unchanged from mother to child, unless there is a mutation. In Fife's case, mDNA from Queen Alexandra passed to his grandmother, Louise, Princess Royal, and then to his mother, Princess Maud of Fife, and then to him. Fife's mDNA was a 98.5 percent match with the bones, a rare imperfect match that scientists suspected was caused by a genetic mutation on the Russian side called a heteroplasmy. In 1994, the remains of Nicholas's younger brother, Grand Duke Georgy Alexandrovich, were exhumed in Saint Petersburg. The mDNA from Grand Duke Georgy also revealed the heteroplasmy, confirming the theory of the mutation and conclusive proof that the bones indeed belonged to the last tsar of Russia.