The Duke and Duchess of Cambridge stunned royal fans with a bold move.

While attending a Coronation Big Lunch, the couple went on an unplanned walkabout.

The Prince of Wales was gifted a mysterious drink from a fan which he sipped from before passing to Kate.

This move broke royal protocol as they're not supposed to accept complimentary food or drink from strangers.

The protocol exists to prevent attempts to poison members of the monarchy.

The couple's actions were surprising considering their status as high-profile members of the royal family.

They later shared adorable photos and videos from the walkabout on Instagram.

The move has sparked a debate about the extent to which the royals should break with tradition.

The incident has left fans wondering what other surprises the Duke and Duchess have in store for the future.