The sneaky way Prince Philip spent the last night of his life

The night before he died, Prince Philip — who had been secretly suffering from prostate cancer for nearly eight years — managed to sneak away and enjoy himself one last time in private.

The 99-year-old royal “gave his nurses the slip … helped himself to a beer and drank it in the Oak Room” of Windsor Castle, according to to the upcoming biography “Queen Elizabeth II: A Personal History” by royal writer Hugo Vickers.

The book is out April 9, the same day Philip died at home in 2021.

On that day, “he got up, had a bath, said he did not feel well and quietly slipped away,” Vickers writes, noting wryly that Philip’s death followed his usual behavior of disappearing without Queen Elizabeth knowing — a so-called Irish goodbye.

“There had often been times in earlier days when the queen had asked the staff to let her know when Prince Philip was leaving,” Vickers writes, “only to be told ‘His Royal Highness left twenty minutes ago.’”

After his death, “she took the line that she was ‘absolutely furious that, as so often in life, he left without saying goodbye.’”

But in the years before his passing, the queen gave her husband “loose rein” — so much so that the couple, married for 73 years, effectively lived “separate” lives, according to the book.

After Philip retired from public duties in 2017, he spent much of his time at Wood Farm, a private, four-bedroom house on the Sandringham Estate in Norfolk, where he was often joined by his longtime confidante Penny Romsey, Countess Mountbatten of Burma.

He made his final solo appearance in August 2017 where he was bid farewell by the Royal Marines.

“After that final engagement, the queen let [him] do exactly as he pleased,” Vickers writes. “He was at his happiest at Wood Farm and he more or less settled there. In the course of the next two and a half years, that was his home. He enjoyed his carriage-driving, read voraciously and painted a little.”

While the queen occasionally visited on weekends, “in a sense they separated.”

Instead, Prince Philip was often joined by another woman, Vickers writes: “Penny Romsey, the new Countess Mountbatten, often stayed with him there.”

According to Ingrid Seward’s 2020 book “Prince Philip Revealed,” Romsey, who was portrayed by Natascha McElhone in “The Crown,” was the “second-most important woman in the Duke of Edinburgh’s life — a constant confidante, loyal companion and ‘keeper of secrets.”

But the COVID-19 pandemic ended the queen and Phillip’s separation, as both quarantined at Windsor Castle with a very skeleton staff looking after their needs.