Mary, Queen of Scots, is famous for being executed by her cousin, Queen Elizabeth I. Before her beheading, Mary wrote a letter to her brother-in-law, Henri III.
The Last Letter of Mary, Queen of Scots

Mary, Queen of Scots, is famous for being executed by her cousin, Queen Elizabeth I. Before her beheading, Mary wrote a letter to her brother-in-law, Henri III.
Marie Antoinette of Austria was the Queen of France who had the bad luck of being consort during the French Revolution. Here is her last letter.