How could you have possibly done that in only 50 years?
1. I started a plot to get a claim on France and waited for it to be completed before accepting England's surrender. That made me the King of England, with a claim on France.
2. I declared war on France, then used a mercenary doomstack to crush France's armies quickly, while taking the counties through attrition. By the time northern France was fully occupied, I managed to force a surrender on the King of France and became the King of England & France.
3. The HRE still had more land than me, that allowed me to get an Invasion casus belli on them. With France and England together, my levies were large enough to beat the HRE back; the Emperor surrendered and the HRE became my primary title.
4. I started the Reconquista on the Iberian Peninsula and pushed vassal claims on Scotland and southern Ireland. The rest of Ireland accepted vassalage without further military intervention; being an Emperor made it possible to get the Dukes to turn over peacefully.
5. I invited pretenders to the crowns of Hungary, Sicily and Croatia to my court, gave them some land in the Empire (by then, Francia, Brittania and the HRE) and pressed their claims; since they were my de jure vassals and I was capable of having Kings as vassals, they stood by me after becoming rulers.
If anything, the surprising bit is that William made it all the way to 89 years, which gave me enough time to change the succession laws for the three Empires. He is 86 in that screenshot.