The nickname was seemingly met in good humour by the King, who appeared to burst out laughing.
He then greeted his younger sister by kissing her hand.
Although they are known for typically adhering to formality, the sweet exchange gave fans a glimpse at what the family members are like behind doors.
Speaking previously on The Telegraph’s Royal Insight YouTube series, the publication’s royal editor Hannah Furniss discussed the “lovely moment”.
Hannah described Charles and Anne as having a “very warm relationship”, adding that the Princess is a key part of her brother’s inner circle.
She added: “She is probably in a better position than anyone to give him advice, give him a bit of sympathy when he needs it, give him a bit of a pep talk.
“She understands how the Royal Family works and she has a bit of an eye to the past and to the future.”