The Grand Duke joined a cult nick-named "the black peril", a group interested in the occult.

They are credited with introducing first a charlatan mystic named merely Philippe, and then, with graver consequences, Grigori Rasputin (1869–1916) to the Imperial family.

Prince Felix Yussupov (1887–1967) – who was their neighbour in Koreiz – once described Znamenka, the Grand Duke and Duchess's palace, as "the central point of the powers of evil".

This was later to be a widely held belief within the higher echelons of the divided Russian court.

Here Grand Duke Peter Nicholaievich died at Cap d'Antibes, near Antibes, on 17 June 1931.