Here also perished with William, Richard, another of the King's sons, whom a woman without rank had borne him, before his accession, a brave youth, and dear to his father from his obedience; Richard d'Avranches, second Earl of Chester, and his brother Otheur; Geoffrey Ridel; Walter of Everci; Geoffrey, archdeacon of Hereford; the Countess of Chester; the king's niece Lucia-Mahaut of Blois; and many others ... No ship ever brought so much misery to England. [Gesta Regum Anglorum]The William mentioned was the only surviving heir of King Henry I of England.
The White Ship was a magnificent vessel that had recently been refurbished with new materials. Its captain was the son of one of William of Normandy's pilots; in fact, the father had piloted William's flagship in the flotilla that conquered England. Had the captain had his way, all might have been well. Here's what happened:
King Henry and his sons were in Normandy, and returning to England. The ship was offered to him for the voyage, but as he had already made arrangements and was ready to depart, he gave the honor of the White Ship to his sons. Henry left for England. The sons, on their own and in command of a fancy ship, were generous in allowing the crew and passengers to start drinking while dockside. Later, with night approaching and alcohol flowing, they decided (foolishly) to set off and beat the king to England; they were sure the ship could do it, despite being weighed down by about 300 bodies. So they set off into the darkness, with a tipsy crew.
The ship hit a rock, tearing a hole in the side. William of Malmesbury's version has one survivor, clinging to the rock all night; Orderic Vitalis says there were two. In either case, we have some details that might be true, such as Prince William escaping in a boat, but going back to rescue his half-sister and having his boat capsized when too many people tried to climb aboard.
Prince William's death forced Henry to name his daughter Matilda his heir. When Henry himself died in 1135, his nephew, Stephen of Blois, decided a firm male ruler for England was more important than honoring the oaths he made to support Matilda. Stephen crossed the Channel to claim the throne, and set off almost two decades of civil war.