When King Louis XVI tried to run away who found out it was him?

This happened op June 20/21, 1791.

Varennes is a very significant episode during the French revolution. King Louis XVI, his wife and children and some servants fled the Tuillerie palace in which they had been put on "house-arrest" after their removal from their palace at Versailles.

Louis XVI eventually decided to flee after Marie Antoinette had been seriously threatened to be murdered and it became obvious that the Revolutionists and the monarchs were not warming up to the idea of constitutional reigning of France (reigned by the Assemble Nationale and Louis XVI together). Marie Antoinette was the one that begged her husband to flee with the family, he eventually caved to the idea. They attempted to flee to Montmédy, Count von Fersen (who was a very close personal friend of Marie Antoinette) made the plan together with the Braon de Bretuil. With a carriage they fled in the middle of the night. They were to meet royal troups in Montmédy who would assist them organize counter revolutionary actions and to restore the monarchy.

Because the berline in which they traveled was so heavily packed it crept towards Montmédy and the trip took too long. When they arrived in the little town Varennes, all of France already knew the royal family had escaped Paris en everybody was on the look out. La Fayette even ordered an arrest warrant. A postmaster called Drouet recognized the king's face while in Varennes (in spite of his disguise) from a 50 livres banknote. La Fayette rushed over and handed the King his arrest warrant and they were escorted back to Paris.