Final answer:
On June 21st, 1791, the king and queen attempted to escape from the palace under the cover of darkness.
Step-by-step explanation:
The phrase "attempted escape of the king and queen" is often associated with the French Revolution, particularly the failed attempt by King Louis XVI and Queen Marie Antoinette to escape from Paris in 1791. This event is known as the Flight to Varennes.
On June 21st, 1791, the king and queen attempted to escape from the palace under the cover of darkness. Louis XVI and Marie Antoinette, along with their children, disguised themselves and tried to leave the Tuileries Palace in Paris to reach the eastern border of France.