If the Duke of Monmouth had succeeded in 1685, nobody today would know about William, Prince of Orange

Check this out. The authorities reported a sighting of James Scott, the Duke of Monmouth, near Dublin in 1683, and wanted him to be apprehended. "they knew by his pretty black brows that it was the Duke of Monmouth, he had seen his pretty sweet face fourty times on the picture on horseback". The Duke and William were a similar age, they were first cousins, with the same grandfather, King Charles I. How history could have been different.

What was 'the picture on horseback'? Below is a 1675 painting of Monmouth, showing him during the 1673 Siege of Maastricht. From the collection of the National Portrait Gallery.