PROLOGUE
"...in late November, Prince William set out with several of his father's courtiers from Barfleur to Pevensey in England, in a ship captained by the son of the man who ferried his grandfather back in 1066. This voyage would always be viewed as something of an embarrassment by King Henry, as William and his friends got stone-cold drunk to celebrate his recent ascension to the Duchy of Normandy, and tried to get the crew to join in on the festivities - thankfully, William's cousin Stephen of Blois [1] provided a firmer hand and kept the crew sober. The prince arrived in England wishing for death due to his hangover and the lecture he would get from his father..."
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[1] This is the POD. OTL, Stephen of Blois - yes, the same guy who fought with Matilda for the crown OTL years later - had intended to travel on the White Ship, but left at the last minute, whether from fear of overcrowding, sea-sickness, or, as one chronicler claimed, explosive diarrhea (seriously), and so was not on board. Here, he stays on and deals with both the drunkenness of the crew and the overcrowding, although the narrator is probably simplifying things. In any event, this allows for the survival of William Adelin (and by extent, Thomas FitzStephen, Richard Fitzroy, Matilda Fitzroy, Geoffrey Ridel, Earl Richard of Chester and his wife Lucia-Mahaut of Blois, and assorted others).