Russian investigators are to exhume the remains of Tsar Alexander III as part of their probe into the authenticity of the remains of his two grandchildren. Tsarevich Alexander and Grand Duchess Maria were shot dead alongside their father, Tsar Nicholas II, and other family members in 1918.

The members of the Russian imperial family who were shot dead by Bolshevik troops after the Russian Revolution are regarded as saints by the Russian Orthodox Church, which has never accepted tests authenticating the remains as valid.

Now the remains of arch-conservative Alexander III, who ruled Russia from 1881 to 1894, will follow those of his son and successor, Nicholas II, and daughter-in-law, Alexandra, in being exhumed from their resting place in St Petersburg's Peter and Paul Fortress.

"At the initiative of His Holiness the Patriarch, a decision has been made to open the tomb of Emperor Alexander III. Everything depends on the technical conditions," senior investigator Vladimir Solovyov told Interfax news agency, adding that the exhumation would likely take place in late November.

The remains of Nicholas II, Alexandra and three of their children were unearthed near the city of Ekaterinburg in 1979, and formally identified in 1991. Those of Alexei and Maria were discovered in 2007, with tests establishing their identity.

The remains of the two were due to be lain to rest alongside their family later this year, but the Orthodox Church insisted on further tests being conducted. In July, Russian Prime Minister Dmitry Medvedev ordered a working group to be set up to examine the authenticity of the remains.

Samples have been taken from the bloodstained coat of Tsar Alexander II, the great grandfather of Alexei and Maria, which he wore when assassinated by anarchist terrorists in 1881, and permission is being sought to examine the remains of Nicholas II's sister, Grand Duchess Elisabeth, which were laid to rest in Israel.