Earl of Mornington used as a courtesy title by the heir apparent to the Marquess of Douro, himself the heir apparent to the Duke of Wellington. As of 2015 the title is held by courtesy by Arthur Wellesley, Earl of Mornington, son of Arthur Wellesley, Marquess of Douro and grandson of Charles Wellesley, 9th Duke of Wellington. The Wesley or Wellesley family descended from Sir Richard de Wellesley (15th century). His grandson Sir William Wellesley (died 1602) lived at Dangan Castle, County Meath. The family estates passed down the male lines. One of Wellesley's daughters, Alison, married John Cusack. Their son Sir Thomas
Richard Wellesley, 1st Marquess Wellesley for many years with Hyacinthe-Gabrielle Roland, an actress at the Palais Royal. She had three sons and two daughters by Wellesley before he married her on 29 November 1794. He moved her to London, where Hyacinthe was generally miserable, as she never learned English and she was scorned by high society: Lady Caroline Lamb was warned by her mother-in-law, Elizabeth Milbanke, a noted judge of what was socially acceptable, that no respectable woman could afford to be seen in Hyacinthe's society. Their children were: Through his eldest daughter Lady Charles Bentinck, Wellesley is a great-great-great grandfather to Queen Elizabeth II.