Queen Elizabeth II was at home at Windsor Castle, the sentries who guard her were on duty, and the large park surrounding the magnificent building was full of tourists.
So it didn't take long for people to realize that something was out of order when a couple enjoying a picnic on the lawn allegedly had too much to drink, stripped naked and began having sex on their blanket.
"One window from the guardroom opened up and when a soldier saw what was going on he told his mates — and lots of windows opened up," witness Mark Robinson told The Sun newspaper.
"The couple did not care who was looking and just kept going as if they were in their own bedroom."
Tourists snap pictures
Japanese tourists filmed the couple, who only stopped when police officers arrived on the scene, witnesses said.
Thames Valley Police said the man and woman were arrested and cautioned for outraging public decency in the Sunday incident.
The queen was in the castle at the time, but her office declined Friday to comment on what had happened.