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This sounds like an urban legend, but make some sense to me

How did the name William get the nickname Bill? – Yahoo! Answers

When William of Orange ruled England, Ireland and Scotland, he was noted for leaving massive debts wherever he went. The proprietors all across the land, knew of his reputation and while they couldn’t refuse the ruler of the land, they knew that after he left they would be laden with many bills to pay…and wherever he went the people would say, “Here comes bills.”