Elizabeth Hay , Countess of Erroll ( 17 January 1801 - 16 January 1856 ; born Elizabeth FitzClarence ) was an illegitimate daughter of King William IV of the United Kingdom and Dorothea Jordan .
Elizabeth Hay , Countess of Erroll ( 17 January 1801 - 16 January 1856 ) , an illegitimate daughter of William IV and Dorothy Jordan , married William Hay on 4 December , 1820 , at the age of 19 .