Where did Robert Stewart get the title Viscount Castlereagh?
From his family's ancient title
From his father
From his courtesy title
From the King
Answer
Robert Stewart was born into the nobility as the third son of the 2nd Marquis of Londonderry. The courtesy title of the eldest son of a marquess is viscount. So, Stewart got the title Viscount Castlereagh from his courtesy title.
The Castlereagh Chronicles: Unraveling the Legacy of Robert Stewart, Viscount Castlereagh