However , in July 1762 his friend , the Czar Peter III , was assassinated in connection with a successful power - grab involving his estranged wife .
He was also a grand duke and commercial legate at the Russian court .
In July 1762 grand duke 's friend , the Czar Peter III , was assassinated in connection with a successful power - grab involving his estranged wife .
He was also a grand duke and commercial legate at the Russian court .