Bells rang in celebration from St. Paul's Cathedral in London Friday to mark the start of the official celebration of Queen Elizabeth II's 90th birthday.

The queen's milestone birthday is being marked with a three-day series of festivities that will include solemn religious events and street parties in many towns and cities.

The celebration has been a lengthy affair, starting with her real birthday in April. The monarch's official birthday is traditionally celebrated in June when Britain's weather can be more favorable.

Elizabeth, dressed in a yellow coat-dress and matching hat, and her husband Prince Philip attended a service of thanksgiving at St. Paul's Friday, on what is Philip's 95th birthday.

She turned to smile at a crowd of well-wishers singing "Happy Birthday" as she climbed the cathedral steps.

They were joined by Prince Charles and his wife Camilla and Prince William and his wife Kate.

Prime Minister David Cameron read from the Gospels, and Archbishop of Canterbury Justin Welby gave the sermon.

Popular naturalist and broadcaster David Attenborough and Paddington Bear creator Michael Bond — who both turn 90 this year — also attended.

The traditional Trooping the Color parade will be held Saturday, the queen's official birthday. The event is expected to draw throngs of Britons and visitors to Buckingham Palace for a possible balcony appearance by the senior royals.

On Sunday, the Mall in front of the palace will host lunch for roughly 10,000 charity workers, patrons and members of the royal family.

Street parties are planned in many locations, including some in Commonwealth countries and also in the United States.

British newspapers have been filled with paeans to the queen, and editorials urging the public to show its gratitude for her long reign.

Philip, who has heart disease, missed an engagement recently due to health issues but is expected to participate throughout the weekend.

After the three-day extravaganza, the queen is expected to turn her attention to the horse racing season and her lengthy summer holiday in Scotland.