Queen Elizabeth II allowed Michelle Obama to put her arm around her during a meeting at Buckingham Palace in April 2009. Members of the public do not touch the monarch without invitation. No one touches the sovereign without protocol being followed. Michelle Obama put her arm around the Queen’s shoulders. The Queen put her arm around Mrs Obama’s waist. The two women stood with their arms around each other. The protocol evaporated.

The meeting took place at the reception during the G20 summit. Michelle Obama, tall, warm, and apparently unconstrained by the specific warnings that American dignitaries are usually given about physical contact with the British monarch, placed her hand on the Queen’s back.

The Queen did not step back. She did not freeze. She placed her arm around Mrs Obama’s waist in return. The two women stood together in a moment of complete informality that no protocol document had anticipated.

The Queen subsequently described royal protocol as “rubbish” to Mrs Obama in a private exchange that Mrs Obama later shared publicly. The specific wording — the Queen calling her own protocol rubbish — has been confirmed in various accounts.

The photographs from the moment show two women who are comfortable with each other. One of them is the sovereign of the United Kingdom. Neither of them is performing a greeting.