Royals Queen Elizabeth 'Remains Totally in Control': 'The Problem Is Physical Mobility,' Says Royal Biographer The image of Prince Charles and Prince William at the State Opening of Parliament offers a glimpse of the future monarchy, but the Queen is still "in charge," says royal historian Robert Lacey By Simon Perry Published on May 10, 2022 08:11 AM Share Tweet Pin Email Queen Elizabeth. Photo: Dominic Lipinski - WPA Pool/Getty The State Opening of Parliament on Tuesday morning saw Prince Charles take on one of the most important duties of his mother Queen Elizabeth. Prince William also received a taste of what his destiny as the future King will be like as he joined the ceremony for the first time. By special order of the Queen, Charles stepped in to give the Queen's Speech at the traditional ceremony after the monarch announced that she was unable to attend amid ongoing mobility issues. "The Queen continues to experience episodic mobility problems, and in consultation with her doctors has reluctantly decided that she will not attend the State Opening of Parliament tomorrow," Buckingham Palace said in a statement on Monday. But the sight of the two immediate heirs to the Queen sitting together at the Houses of Parliament is more about showing the line of succession rather than indicating Charles is set to take on more of his mother's constitutional powers. Royal historian and biographer Robert Lacey calls Tuesday's ceremony, which also saw Charles' wife, Camilla, Duchess of Cornwall, seated beside him, an "enormously significant moment." Prince William, Prince Charles and Camilla, Duchess of Cornwall. BEN STANSALL/POOL/AFP via Getty Images "She's clearly thinking of the future and this can be seen alongside the moment she said it was her wish that Camilla be known as Queen Consort, which was another important development this year," Lacey tells PEOPLE. "Asking her son Charles and William to attend is clearly about succession, about emphasizing a partnership and teamwork," he says. Prince Charles Gives the Queen's Speech for First Time at Opening of Parliament After Monarch Bows Out But it stops short of a regency, in which the powers of the Sovereign are formally transferred to the heir because of incapacity. "Regency involves a surrender of constitutional authority, which is very much not happening in this case," Lacey says. The royals at the State Opening of Parliament. HANNAH MCKAY/POOL/AFP via Getty Images Charles — like his mother — doesn't write the speech. That's a role of the U.K. government led by Prime Minister Boris Johnson, as it outlines the administration's upcoming legislation. "Charles is deputizing for the Queen, as he has done before — and as William and Kate have also started to do in some of the duties they've been doing," Lacey adds. The only time a regency has been instituted was for George III who was deemed mentally incapable of carrying out the duties of state. "The sense I get from everyone I speak to is that the Queen remains totally in control of her faculties and of everything at the palace," he adds. "The problem is physical mobility — and that is not a constitutional or regency issue. She is in charge." Prince Charles. ALASTAIR GRANT/POOL/AFP via Getty Images The paradox she faces is that while she can walk, it's very likely that she's worried she might stumble, "and the symbolism of her doing that is so enormous that she would not want to put herself in that situation," Lacey adds. The Queen has been experiencing mobility issues in recent months and finds it difficult to stand for long periods. Her Majesty 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!" She also recently shared a small glimpse into her battle with COVID-19 earlier this year, revealing that "it does leave one feeling very tired and exhausted." Queen Elizabeth. Richard Pohle - WPA Pool/Getty Images 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! The Queen delegated her royal duty of opening a new session of Parliament to her son and grandson via a letter patent, which enables the Prince of Wales and the Duke of Cambridge to jointly exercise that function. No other functions have been delegated by Her Majesty, according to the palace. While she wasn't able to attend Tuesday's ceremony, the Queen has a busy schedule this week. She undertook a call with Australia on Monday and has a planned Privy Council and Prime Minister audience on Wednesday. She's also expected to undertake some private engagements later in the week, according to the palace.