As the Queen arrived in Norfolk to begin her festive break, it emerged her husband, Prince Philip, had been admitted to hospital.
The 93-year-old monarch arrived at King's Lynn by scheduled train from London King's Cross, arriving on time just after 12.30pm.
Soon after she departed by car for the final leg of her journey to Sandringham, royal aides confirmed her husband, the Duke of Edinburgh, was in hospital to be treated for a "pre-existing condition".
Prince Philip left Sandringham, where he spends much of his time since retiring, to attend the King Edward VII Hospital in London this morning.
A Buckingham Palace statement said: "The Duke of Edinburgh travelled from Norfolk this morning to the King Edward VII Hospital in London for observation and treatment in relation to a pre-existing condition.
"The admission is a precautionary measure, on the advice of His Royal Highness' Doctor."
The Duke is expected to be in hospital for a few days. He was not taken by ambulance and it was a planned admission.
The announcement was made just before 2pm, shortly after the Queen, who caught the 10.42am Great Northern service from King's Cross station in London, arrived at platform two in King's Lynn at 12.31pm.
Fellow passengers didn't realise who was in the First Class carriage near the front of the train.
The Queen, accompanied by protection officers, usually catches up on correspondence from her red box during the 1hr 50m ride to Lynn.
She is believed to have bought a £60 first class single ticket for the journey.
Carrying a back handbag and wearing a pink coat with patterned headscarf, the 93-year-old monarch was greeted by station manager Graham Pratt, who accompanied her on the short walk to her waiting car.
Passenger Monika Saganowska, 25, who boarded the train at Watlington, the stop before King's Lynn, said she was unaware the Queen was on board until she arrived at King's Lynn and saw police on the platform.
"I think it's great actually," said Ms Saganowska. "I always thought she would have some kind of a private train or at least a carriage or something, but I didn't know that she was taking the public train which I think is great."
The Queen was driven to final 10 miles or so to Sandringham - via part of the A149 coast road named after her - where she will oversee preparations for the Royal Family's traditional Christmas break in Norfolk.
MORE - Which Royal Family members are coming to Sandringham for Christmas
They include choosing a Christmas tree from her sawmill and finalising menus.
Thousands of well-wishers are expected to pack into Sandringham Park on Christmas Day, when the Queen and family members attend morning service at the Church of St Mary Magdalene on the estate.
MORE - How the Royal Family spends Christmas
The Queen is expected to stay in Norfolk until February 6 - the anniversary of her father King George VI's death at Sandringham in 1952, after which she acceded to the throne.
Security was tight at the station before the Queen's train arrived just after 12.30pm. Police searched platforms and other areas using sniffer dogs.
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