Royals Queen Elizabeth Lights the Platinum Jubilee Beacon with Help from Grandson Prince William! The "Tree of Trees," which is made up of 70 potted mini trees, was illuminated outside Buckingham Palace in honor of Queen Elizabeth By Simon Perry and Erin Hill Erin Hill Twitter Senior News Editor, PEOPLE People Editorial Guidelines Published on June 2, 2022 04:48 PM Share Tweet Pin Email Queen Elizabeth's Platinum Jubilee celebration is officially lit! The 96-year-old monarch kicked off her four-day celebration with Trooping the Colour on Thursday morning. And she's ending the day with a special dual beacon lighting ceremony with Prince William. The Queen led the lighting of the Principal Platinum Jubilee Beacon from Windsor Castle, while her grandson William represented her at Buckingham Palace, where the beacon was officially lit. With a symbolic touch of the Commonwealth Globe of Nations, which was placed on a podium, the Queen set off a chain of lights leading to the Principal Beacon outside Buckingham Palace. The beacon takes the form of a sculpture dubbed the "Tree of Trees," which stands 70 ft. tall in honor of the Queen and her astonishing 70 years on the throne. Around 3,000 beacons, including fires and gaslit torches, will be lit around the U.K. at the same time. The Queen stepped out in the Quadrangle of Windsor Castle for the lighting ceremony and was received by beacon pageant master Bruno Peek, who has overseen the Platinum Jubilee Beacons Project. Queen Elizabeth at the beacon lighting ceremony. ADRIAN DENNIS/getty Simultaneously, outside Buckingham Palace, the Duke of Cambridge was met by the Chair of The Queen's Green Canopy, Sir Nicholas Bacon, and the designer of the "Tree of Trees," Thomas Heatherwick, to hear about how the sculpture was created. Schoolchildren who have taken part in The Queen's Green Canopy Junior Forester Award were also present, as well as young leaders from Scouts, Girlguiding and the Queen's Commonwealth Trust, who have all been involved with the Platinum Jubilee Beacons Project. Prince William. Chris Jackson /getty Peek says the number of beacons across the country has easily surpassed his target of 1,500. Beacons are also being lit across the Commonwealth — from Tonga to India and Rwanda. Queen Elizabeth 'Remains Totally in Control': 'The Problem Is Physical Mobility,' Says Royal Biographer "She's our country, our nation, and our Commonwealth, and I believe she's the person that everybody really looks up to," Peek, 70, told PEOPLE of how the Queen is viewed across the world. "She's got such continuity." Queen Elizabeth. ADRIAN DENNIS/getty "She's just got that humility. She knows it's not about her. She knows it's about — this is my humble opinion — about her position and the responsibility she's got. I mean, responsibility, even now at her age must be phenomenal," he added. Can't get enough of PEOPLE's Royals coverage? Sign up for our free Royals newsletter to get the latest updates on Kate Middleton, Meghan Markle and more! Designed by Thomas Heatherwick, the tree (and its 80 branches) "stands tall as a message of hope, regeneration and optimism to the nation and the world," stated a press release from the Queen's Green Canopy, which commissioned the sculpture and organized a magnificent tree-planting effort across the U.K. this year. More than one million trees have been planted across the U.K. (including by Kate Middleton and Prince William in Wales) to create a lasting legacy in the Jubilee year. Prince William. Chris Jackson /getty Beacons were traditionally used by communities to send warnings of war or other important messages to neighbors. But since Queen Victoria's Diamond Jubilee, they have been used during national celebrations for monarchs. For more on the Queen's Platinum Jubilee, listen below to our daily podcast PEOPLE Every Day. "The one thing about beacons is that you can bring people of all ages, all nationalities, all religions — it doesn't matter who you are you can bring them together at one moment in time to celebrate an important anniversary," Peek said. "That's why they've always been successful in Jubilees." After a busy day of outings, the Queen announced that she will not be attending Friday's National Service of Thanksgiving at St. Paul's Cathedral. Prince William. Chris Jackson /getty "The Queen greatly enjoyed today's Birthday Parade and Flypast but did experience some discomfort," a spokesperson for Buckingham Palace said on Thursday. "Taking into account the journey and activity required to participate in tomorrow's National Service of Thanksgiving at St Paul's Cathedral, Her Majesty with great reluctance has concluded that she will not attend," the statement continued. Queen Elizabeth, Prince Louis, Kate Middleton, Princess Charlotte, Prince George and Prince William. Chris Jackson/Getty Images "The Queen is looking forward to participating in tonight's Beacon lighting event at Windsor Castle and would like to thank all those who made today such a memorable occasion." The Queen has been experiencing mobility issues in recent months and finds it difficult to stand for long periods. She has been using a walking cane and even complained about mobility problems, joking during an in-person meeting: "Well, as you can see, I can't move!" Friday's Service of Thanksgiving will be attended by several members of the royal family, including Prince Harry and Meghan Markle, who traveled from their home in California for the Platinum Jubilee.