On what date was the Duchess of Richmond's ball held in Brussels?

On what date was the Duchess of Richmond's ball held in Brussels? It was held on 15 June 1815.

The ball took place on the evening of 15 June 1815, in Brussels, just as Napoleon's Hundred Days campaign was turning into a major Allied emergency. It was held in a coach house adjoining the temporary Brussels residence of the Duke and Duchess of Richmond. The event was both a fashionable gathering and an important moment in the opening of the Waterloo campaign.

News of the French advance interrupted the evening. Wellington and his officers learned that Napoleon had crossed into the United Kingdom of the Netherlands and that fighting was imminent around Quatre Bras. Officers left the ball to rejoin their units, and the next day's Battle of Quatre Bras began on 16 June.

The date is frequently confused with 16 or 18 June. Quatre Bras was fought on 16 June, the Battle of Waterloo on 18 June, and the ball came two nights before Waterloo, on 15 June. That sequence explains why the event is remembered as the dramatic “eve” of the campaign's first major clashes.