In this TL Mary Stuart does not suffer a miscarriage after marrying William the 3rd. Instead she gives birth to a live if unhealthy child called William. Therefore upon the death of his father William the 4th becomes king of Great Britain and Stadholder of the United Provinces (After overthrowing Regent John William Friso). However, the crowns are not yet united as William the 4th is determined to keep the two nations separate, controlling the United Provinces himself while leaving his wife Amelia to act as Queen of Great Britain.