At first glance there was nothing out of the ordinary as an elderly lady boarded the 10.45am train from Kings Cross on Thursday.
But a closer look revealed the passenger, her head covered with a headscarf, was in fact the Queen.
The British monarch, accompanied by minimal security, was on her way to Sandringham for her Christmas break. She was to join Prince Philip, who travelled up separately on Wednesday.
And rather than take the Royal Train – which costs an estimated £57,142 for each journey, the cost-cutting monarch chose to take public transport instead.
She did travel first class though, and royal protection officers stopped other passengers from coming into her section of the train.
But officials insisted the 12-seat coach would have been opened up to fellow travellers if the other first class compartment had become crowded.
Reps for the train company confirmed the Queen, who spent some of the journey opening her Christmas cards, had not been given any special treatment. They also said her tickets had been purchased in advance.
A Buckingham Palace spokesman said: "Members of the royal family, including the Queen, frequently use scheduled train services.
"We have to look at issues such as cost effectiveness and security but do try to when it is appropriate."