Blaise Mettreveli made history earlier this month after being appointed as the first woman to head the British Secret Intelligence Service (MI6).
But, according to German archives cited by the Daily Mail, her grandfather, Constantine Dobrowolski, was a Nazi spy.
Dobrowolski was a Ukrainian who reportedly deserted from the Red Army to become a trusted Nazi informant in the Chernihiv region.
According to reports, Mettreveli never met her paternal grandfather, as he had lived in Nazi-occupied Ukraine.
Documents stored in Freiburg, Germany, describe how Dobrowolski was identified as "Agent 30" by his Nazi commanders.
Born in 1906 to a German-Polish father and a Ukrainian mother, he is believed to have hated the Soviet Union. He joined the Nazis in 1941 and was paid what today translates to around £250 a month for his services as a spy.
Also, according to the same source, there is evidence of his involvement in the looting of the bodies of Holocaust victims and in mocking sexual assaults on female prisoners.
The Soviets had placed a bounty on Dobrowolski's capture, which would be worth around £200,000 today, declaring him the "greatest enemy of the Ukrainian people".
Meanwhile, Mettreveli, who joined the British Secret Service in 1999 and has spent most of her career on operations in the Middle East and Europe, is said to have never had contact with her grandfather and did not know him.