Rationale
The Act was proposed by George III as a direct result of the marriage of his brother, Prince Henry, Duke of Cumberland and Strathearn, who, in 1771, had married the commoner Mrs Anne Horton, the daughter of Simon Luttrell and the widow of Christopher Horton. Royal Assent was given to the Act on 1 April 1772, and it was only on 13 September following that the King learned that another brother, Prince William Henry, Duke of Gloucester and Edinburgh, had in 1766 secretly married Maria, the illegitimate daughter of Sir Edward Walpole and the widow of the 2nd Earl Waldegrave. Both alliances were considered highly unsuitable by the King, who "saw himself as having been forced to marry for purely dynastic reasons".
Read more about this topic: Royal Marriages Act 1772