By Bryony Jones
LONDON (CNN) — Queen Elizabeth II’s Diamond Jubilee celebrations will reach a climax Tuesday — but the monarch’s elderly husband, Prince Philip was not at her side as she arrived at St Paul’s Cathedral for the service of thanksgiving.
Prince Philip was recovering at King Edward VII Hospital with a bladder infection, where he is expected to remain under observation for several days. “He is, understandably, disappointed,” the queen’s press secretary said in a statement.
The service is the climax of four days of celebrations to mark the queen's 60-year reign. It will be followed by a carriage procession through the streets of London and a flypast over Buckingham Palace in the afternoon.
On her arrival the queen was heralded by a fanfare of trumpets and cheered by thousands of well-wishers. Before the service a long line of people in their "Sunday Best" -- women in their poshest frocks and biggest hats, men in morning suits and military uniforms -- snaked across Paternoster Square and around behind the cathedral ahead of the service. Outside, thousands of well-wishers crowded against the security barriers, flags at the ready, cheering as every bus full of new arrivals arrived at St Paul's.
The Duke of Edinburgh had been at the queen's side throughout the lengthy jubilee pageant on the Thames on Sunday, as heavy rain lashed the seven-mile flotilla along the river. His illness, which was announced Monday night, meant he was not able to attend last night's pop concert at Buckingham Palace.
Outside the cathedral Pip Sweetman, from Portsmouth, southern England, said she had come to London with her father, one of the guests invited to St Paul's. "He's in there somewhere -- I only hope he's turned his phone off," she said. "I also wanted to support the queen -- I suppose she's feeling a bit lost today, without Prince Philip."
Tuesday's events begin with the service at St Paul's -- site of Prince Charles and Princess Diana's wedding in 1981 -- led by the Dean of St Paul's and with a sermon preached by the Archbishop of Canterbury.
The Dean, the Very Reverend David Ison, is expected to give thanks "for the prosperous reign of the queen" and for her decades of "loyal service and commitment."
The queen, Prince Charles and the Duchess of Cornwall, the Duke and Duchess of Cambridge and Prince Harry will attend the service, alongside other royals.
British Prime Minister David Cameron will give a reading, and several new pieces of music, specially commissioned for the jubilee, will make their public debut.
A small demonstration by an anti-monarchist group was dwarfed by the hordes of royal supporters, but still took a prime spot in front of St Paul's, where a long-running Occupy protest took place earlier this year.
Graham Smith, CEO of pressure group Republic, admitted the demonstrators were truly outnumbered, but insisted their presence at the event was important.
"We are here to make sure that the millions of people in the country who oppose the monarchy have their opinions heard," he told CNN. "It is only a token protest, but we're here so the monarchy don't get away with thinking that the whole country is in love with them."
But as the queen arrived, the republican's shouts of "Make monarchy history!" were drowned out by deafening shouts of "God save the queen!"
Following the service, members of the royal family will attend a receptions in the City of London, and a lunch at Westminster Hall, before taking part in a procession from Westminster to Buckingham Palace.
Members of the three armed services, military bands and huge crowds of well-wishers are expected to line the route as the royals make their way through the city.
The queen and the Duke of Edinburgh had been expected to travel together in the 1902 State Landau, the horse-drawn open-top carriage used by the Duke and Duchess of Cambridge following their wedding at Westminster Abbey last year. It is not clear who will accompany the queen in Prince Philip's absence.
Once back at the Palace, the royal family will appear on the balcony to watch a flypast by aircraft from the Battle of Britain -- including a Dakota, a Lancaster bomber, Spitfires and a Hurricane -- and the Red Arrows display team.
Squadron Leader Ian Smith, the officer in command of the Battle of Britain Memorial Flight, said the group was honored to be taking part in the jubilee event.
"As a service, the RAF is enormously proud of its heritage, and the opportunity to fly over Buckingham Palace for Her Majesty with the nation's aviation heritage is something that will remain with us for the rest of our lives," he said.
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