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 Harry and his wife Meghan, the Duke and Duchess of Sussex, will join royal family members to watch Trooping the Color from a Buckingham Palace office that overlooks the parade ground, a spokesperson for the duke and duchess told ABC News.

The Sussexes look forward to watching from the Major General’s Office, the spokesperson said.

Senior working members of the royal family, including Harry’s brother, Prince William, and his wife Kate, along with their three children, will watch Trooping the Color, also called the Queen’s Birthday Parade, from the balcony of Buckingham Palace, alongside Queen Elizabeth II herself.

Because they are no longer senior working royals, Harry and Meghan are not part of the traditional balcony appearance, a decision made earlier this year by the queen, according to Buckingham Palace.