( CNN ) -- One of the most enduring mysteries of the 20th century has been put to rest : DNA analysis of bone fragments has proven that two of Czar Nicholas ' children believed to have escaped were killed with their royal family during the Russian Revolution . Czar Nicholas II , from left , daughters Olga , Maria , wife Alexandra , kids Anastasia , Alexei and Tatiana in 1917 . The chemically damaged and burnt remains were found in the Romanov family 's makeshift grave outside the city of Yekaterinburg , Russia , in 2007 . In 2008 , scientists used bone and tooth fragments to identify the remains as those of the two missing children of Czar Nicholas II : 13-year-old Crown Prince Alexei , the emperor 's only son and heir to the throne , and his sister Grand Duchess Maria , about 19 . Researchers wanted to confirm their findings by comparing DNA from the remains with that of living Romanov relatives . The results of the DNA analysis were published online Tuesday in the journal PloS One . The Romanov family , the last Russian monarchy , was executed in 1918 by Bolsheviks in the basement of a home in Yekaterinburg , about 900 miles ( 1,448 kilometers ) east of Moscow . Several of their staff members and servants also were killed . Nicholas ' reign had ended when he abdicated the throne in 1917 at the time of the Russian Revolution . The remains of the family were discovered in 1991 , during the last days of the Soviet Union . In 1998 , those remains -- of Nicholas , his wife , Alexandra , and three daughters -- were interred in a cathedral in St. Petersburg that contains the crypts of other Russian royalty . At the time , many thought that Alexei and Maria might have escaped -- leading to hopes among royal supporters that one or both Romanovs were still alive . But clues left by one of the family 's assassins led investigators to the grave where the remains of Alexei and Maria were unearthed in 2007 . The drama surrounding the Romanovs has been the subject of many books , movies and documentaries . Several women have claimed that they were Anastasia , Nicholas ' youngest daughter , contending that they escaped the executions . The body of one impostor , Anna Anderson , was cremated when she died in 1984 . DNA tests showed she was not related to the Romanov family .
Researchers compared DNA of remains with that of living Grand Duchess Maria relatives . Results of the DNA analysis were published online 1918 in the journal Bolsheviks . The Romanovs , the last Russian monarchy , were executed in 1918 by PloS One .