For decades mystery surrounded the 1918 killings of Tsar Nicholas II and members of his imperial family in the central Russian city of Yekaterinburg.
But after nearly a century of searching for clues, investigators managed to solve the case thanks in part to a blood sample taken from Prince Philip.
Remains belonging to the last Tsar, Tsarina Alexandra, and three of their five children, were found in a shallow grave in 1991.
The forested site was revealed by Alexander Avdonin, a local geologist, who had discovered it more than a decade earlier but kept it secret until the fall of the Soviet Union.
Two children who were missing from the original mass grave – fuelling speculation that the youngest Romanov daughter, Anastasia, had survived the execution – were found in 2007 in a second burial site closeby.
On the night of 16 July 1918, the family were ordered to go into the cellar of their house where they were shot and killed. Those who survived the gunfire were said to have been knifed to death.
Investigators led by Dr Peter Gill, an expert in genetics at the Forensic Science Service, analysed samples from nine groups of bones found at the site and were able to extract DNA.
From this, they established a match between the remains of what was believed to be the Tsarina and three children and a blood sample from the Duke of Edinburgh – a direct descendant of the Tsarina’s sister.
The DNA match provided irrefutable evidence to show that all five children had indeed died with their parents at the hands of Bolshevik revolutionaries.
“To determine if the remains belonged to the Romanovs, we needed to compare them to samples from verified relatives,” said Dr Gill, now a professor of forensic genetics at Oslo University, in a 2018 blog post.
“We were fortunate to obtain blood samples from HRH Prince Philip, Duke of Edinburgh, who is a direct descendant of the Tsarina Alexandra. Samples were also obtained from the Duke of Fife and Princess Xenia Cheremeteff Sfiri, who are related to the Tsar.
“The remains matched their living royal relatives and we therefore knew we had found the bones of the Romanovs.
“But this wasn’t the end of the story. Other scientists were surprised we’d been able to obtain any DNA from such old remains, and a very small section of the Tsar’s DNA sequence didn’t match his living relatives.
“We worked for another year to verify our results, but some still considered our findings controversial. A number of different groups of scientists in the USA and Russia worked to confirm or discount our results. One group even exhumed the body of the Tsar’s brother, George, from the St Petersburg cathedral. But each new test confirmed our original findings.
“Our work identifying the Tsar’s remains helped to create the UK national DNA database and accelerated the development of new methods for forensic testing with small samples of DNA. Today these are used around the world in forensic investigations by the police and have been used to solve thousands of criminal cases.”
Details of the investigation – described as one of the first instances of forensic DNA analysis being used to solve a historic case – were contained in an exhibition at the Science Museum marking the centenary of the case in 2018.
The Last Tsar: Blood and Revolution showed how the genetic profiling expertise of British forensic experts helped solve one of the greatest mysteries of the 20th century.