Queen Elizabeth II shared a written thank you message on Sunday to mark the end of four days of celebrations for her Platinum Jubilee.

"When it comes to how to mark seventy years as your Queen, there is no guidebook to follow. It really is a first. But I have been humbled and deeply touched that so many people have taken to the streets to celebrate my Platinum Jubilee," Elizabeth wrote. "While I may not have attended every event in person, my heart has been with you all; and I remain committed to serving you to the best of my ability, supported by my family."

"I have been inspired by the kindness, joy and kinship that has been so evident in recent days, and I hope this renewed sense of togetherness will be felt for many years to come," the queen continued. "I thank you most sincerely for your good wishes and for the part you have all played in these happy celebrations."

The queen signed her message with her first name, Elizabeth, followed by the letter R, which stands for Regina, the Latin word for queen.

Queen Elizabeth II made a surprise appearance on the balcony of Buckingham Palace Sunday at the conclusion of the four-day celebration of her Platinum Jubilee.

The queen was joined on the balcony by her heirs, Princes Charles, William and George, as well as Camilla, Duchess of Cornwall, Kate, Duchess of Cambridge and Princess Charlotte and Prince Louis.

Elizabeth, dressed in a green coat, green hat and white gloves, stood and watched as thousands of members of the public sang "God Save the Queen."

Before departing the balcony, Elizabeth gave a royal wave.

Music star Ed Sheeran is center-stage in front of Buckingham Palace for the finale of Queen Elizabeth II’s four-day Platinum Jubilee celebration.

As Sheeran performs his hit song "Perfect," images of the queen from throughout her 70-year reign are projected onto screens.

Elizabeth is back in residence at Buckingham Palace after spending much of her jubilee celebration at Windsor Castle. As the Platinum Jubilee Pageant was taking place outside of the palace, the Royal Standard was raised, signifying the queen’s return.

Queen Elizabeth II is back at Buckingham Palace Sunday after spending much of the Platinum Jubilee weekend at Windsor Castle.

The 96-year-old queen has made two in-person appearances during the celebrations of her 70-year reign, at Trooping the Color on Thursday and later that night at the lighting of the Platinum Jubilee beacon.

Elizabeth's return Sunday to Buckingham Palace was marked by the raising of the Royal Standard, the flag flown when the queen is in residence.

Outside the palace, the Platinum Jubilee pageant is taking place, a cultural celebration involving thousands of performers.

Prince William and Kate, the Duke and Duchess of Cambridge, have entered St. Paul’s Cathedral to attend the service.

Several minutes after their arrival, Prince Charles, the heir to the British throne, and his wife Camilla, Duchess of Cornwall, also made their way into the central London cathedral.

Once inside the cathedral, Charles and Camilla joined William and Kate to form a royal procession before they took their seats for the service.

Other royal family members who already arrived include the queen's daughter, Princess Anne, and her husband Vice Admiral Timothy Laurence; their children Zara Tindall and Peter Phillips, and Zara's husband Mike Tindall; and Elizabeth's youngest son Prince Edward and his family.

Prince Andrew's children, Princess Beatrice and Princess Eugenie, as well as their husbands, Edoardo Mapelli Mozzi and Jack Brooksbank, were also in attendance.

The royal family is attending the National Service of Thanksgiving -- which includes Bible readings, prayers and hymns intended to give thanks for the queen's 70-year reign -- without Elizabeth herself. Buckingham Palace announced Thursday that the queen would not attend in person after experiencing “some discomfort” at the Trooping the Color parade earlier in the day.