The mother of Mikhail Khodorkovsky, Marina Khodorkovskaya, has died aged 79.
Russian media reports said she died on August 3 in a Berlin clinic where she was undergoing treatment for cancer.
Khodorkovsky, the former chairman of the now disbanded Yukos oil company and once Russia's richest man, was jailed in 2003 on tax evasion and embezzlement charges widely seen as politically motivated.
After spending 10 years behind bars, he was pardoned and released in December 2013.
Khodorkovsky flew to Berlin shortly after he was released.
