Grand Duke Leon Petrovich Romanov was born in 1882. Like all Russian aristocracy, he was educated at home by various Russian and foreign teachers and lecturers. He was forced to flee Russia after the revolution.
Petrovich meets with Thomas Shelby to pay him for the murder of Anton Kaledin as well as for future business transactions that will occur between them. He informs him that Tatiana is his niece and also that their appearance as a poor family in debt to the King is a facade. They are in fact very rich and simply hide their wealth from the government.
In Episode 3.2, it is revealed that Petrovich plans to kill Thomas once he is done getting what he wants from him.