According to the Duke of Sussex's memoir 'Spare', King Charles was
believed to have been purposely placed in the audience during Prince Harry's
annual school play.
The Duke of Sussex describes in his book how his father grabbed the audience's attention by laughing at inappropriate times during the performance.
This caused confusion among the audience, who thought King Charles was part of the show. Backstage, King Charles praised Prince Harry's performance, but Harry was frustrated that his father had laughed at the wrong times.
When Harry questioned him about it, King Charles seemed baffled and had no idea what Harry was talking about.