Prince William and Kate Middleton pictured in August.

The weight of increasing responsibility rested heavily on Prince William Saturday as Buckingham Palace issued its official update to the British monarchy’s line of succession in the wake of the death of Queen Elizabeth II.

The somber new Prince of Wales, eldest son of King Charles III and now the immediate heir to the throne, stood stoically on the dais as his father was proclaimed the UK’s reigning monarch.

A few hours later, his official Twitter account posted a mournful statement about the loss of his “Grannie.”

“I thank her on behalf of my generation for providing an example of service and dignity in public life that was from a different age, but relevant to us all,” he wrote — pledging to “honour her memory by supporting my father, The King, in every way I can.”

“One day I will lead the family,” William recently told the Sunday Times of London. “And it’s important that I am able to do that.”

But major changes are in store for him, his wife Kate Middleton, and their young children — now to be styled Prince George of Wales, 9, Princess Charlotte of Wales, 7, and Prince Louis of Wales, 4.

William, Kate, and their three children recently moved from London to Windsor.

Just weeks ago, William and Kate moved their family from London to Adelaide Cottage in Windsor, hoping to spend more time with the queen as her health failed and to shield the children from the public spotlight.

Now, though, they will be more under the microscope than ever, taking center stage at a lengthy list of royal ceremonies in the coming weeks and months including the queen’s funeral and the new king’s coronation.

The Waleses will likely move into Windsor Castle, with King Charles expected to divide his time between Buckingham Palace, Sandringham in Norfolk, and Birkhall in Scotland.

The way they were: Prince William and Kate once shared a closer bond with Prince Harry.

William’s relationship with his grandmother “massively improved” in the years just prior to her death, he told the Sunday Times — as he helped her and his father navigate the fraught departure of his brother Harry and wife Meghan Markle from their roles as working royals, as well as the fallout from Prince Andrew’s involvement in the Jeffrey Epstein scandal.

“I think because I’m learning more from her and our views on the future, together with my father, are more aligned than ever,” he said in a recent interview.

Charles and William, too, have experienced a “renaissance” in their once-strained bond, friends say.

The future of the monarchy now rests with William and Kate, the Prince and Princess of Wales.

Meanwhile, Princess Kate — who, as Princess of Wales, takes on the title last held by the beloved Princess Diana — “has been a hugely important factor in him coming to terms with his destiny,” a royal source close to the couple told the outlet.

As a friend said: “Marriage maketh the man. Catherine’s groundedness has been the critical anchor.”

William now takes over the family business of running the Duchy of Cornwall, a 130,000-acre estate that rakes in about $24 million a year — cash used to fund the royal family’s official work.

The couple are tipped to move into Windsor Castle as King Charles settles into Buckingham Palace.
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In November, the new Prince and Princess of Wales will visit the US to champion the Earthshot Prize, a ten-year global environmental initiative they see as their “legacy project.”

“He knows the future [of the monarchy] rests on his, Catherine’s and his kids’ shoulders,” a friend said. “He is going to step up and deliver.”