Sophia Sidney, Baroness De L'Isle and Dudley

Sophia Sidney, Baroness De L'Isle and Dudley (née FitzClarence; 4 March 1795 – 10 April 1837) was the eldest illegitimate daughter of William IV of the United Kingdom and his longtime mistress Dorothea Jordan. She was married to Philip Sidney, 1st Baron De L'Isle and Dudley, and had four surviving children. Shortly before her death in 1837, she served as State Housekeeper in Kensington Palace.

Sophia FitzClarence was born on 4 March 1795 on Somerset Street in London, the eldest daughter of Prince William, Duke of Clarence, by his longtime mistress, the comic actress Dorothea Jordan. Sophia would come to have nine siblings, five brothers and four sisters all surnamed FitzClarence. While circumstances prevented the couple from ever marrying, for twenty years William and Dorothea enjoyed domestic stability and were devoted to their children. In 1797, they moved from Clarence Lodge to Bushy House, residing at the Teddington residence until 1807. The couple separated in 1811 as William sought to produce legitimate issue.

On 13 August 1825, she married Philip Sidney, later an M.P. and the 1st Baron De L'Isle and Dudley of Penshurst in the County of Kent. Sidney was a relation of the Romantic poet and philosopher Percy Bysshe Shelley, though he opted to drop "Shelley" from his surname.

Sophia and her husband had four surviving children, three daughters and a son:

In May 1831 Sophia, like her sisters, was raised to the status of a daughter of a marquess. In January 1837, she was appointed State Housekeeper of Kensington Palace, where she died three months later. Sophia died in childbirth just after drawing a sketch of her ailing father. She was his favourite child and her death caused him intense grief. She was remembered as a woman of great wit, charm and gaiety. There is a memorial to her at St John the Baptist, Penshurst.