Lady Mary Tudor (16 October 1673 – 5 November 1726), by marriage Countess of Derwentwater, was an actress and illegitimate daughter of King Charles II of England by his mistress, Mary "Moll" Davies, an actress and singer. The King's fourteenth child, she was also his last.
By royal warrants, she was granted the surname Tudor and the precedence of a duke’s daughter, and in 1687, aged 14, she was married to Edward Radclyffe, 2nd Earl of Derwentwater, head of a leading northern Catholic family. Through this marriage, she became the mother of James Radclyffe, 3rd Earl of Derwentwater, executed for his part in the Jacobite rising of 1715, and Charles Radclyffe, later executed after the Jacobite rising of 1745. In the aftermath of James's execution and the forfeiture of the Derwentwater estates, she petitioned the Crown and Parliament for clemency and to secure the conversion of her eight-year-old grandson to the Church of England, an attempt opposed by his mother, Anna Maria Webb, who removed him to the Continent.