Royal fans camped out on The Mall ahead of Saturday’s coronation got a royal surprise Friday when they were greeted by King Charles III, Prince William and Kate, the Princess of Wales.

The trio stepped out of their cars and did a walkabout, taking selfies with and shaking the hands of fans who lined the path one day ahead of the coronation service.

Charles and Camilla, the Queen Consort, will travel the same path tomorrow in a procession that will take them to and from Buckingham Palace and Westminster Abbey.

Coronation buzz is spreading across London as the city prepares for the once-in-a-generation event.

Tens of thousands of people -- including the 2,000 people attending the coronation service itself -- are expected to stream into the city for the celebration.

For the past several weeks, workers have been seen cleaning Buckingham Palace and other landmarks, building grandstand seating areas for viewers and hanging flags across the city. In the darkness early Wednesday, coronation participants held a full-dress rehearsal for the big day.

Security is also tight all around London as officials brace for expected anti-monarchy protests.

Royal watchers viewing the coronation will notice three members of Charles’ family missing from today’s festivities.

Harry’s wife, Meghan, the Duchess of Sussex, and their two children, Prince Archie and Princess Lilibet, did not attend the coronation.

Instead, they are home in California, where the family now lives full-time.

Today is Archie’s fourth birthday and Harry is expected to leave shortly after the coronation service to return home to his family.

As a non-working royal, Harry, who sat near his cousins Beatrice and Eugenie inside Westminster Abbey, did not join other members of the royal family in the procession back to Buckingham Palace.