When President Donald J. Trump visited Britain in 2019, British officials arranged for him to have afternoon tea with Charles, then the Prince of Wales, at his London residence, Clarence House. The thinking among British diplomats was that the 70-something heir to the throne would be a good partner for the 70-something heir to a real estate fortune.

It was not clear that Mr. Trump, now 78, and Charles, now 76, had much in common, beyond age and inherited wealth.

But the British were on to something in trying to deepen the personal ties between Mr. Trump and the royal family. He already regarded Queen Elizabeth II, the king’s mother, with a reverence bordering on awe. His visit to Buckingham Palace ranked as one of the highlights of his first term.

With the Trump restoration imminent and the British government now led by a left-of-center prime minister, Keir Starmer, who could find himself politically at odds with Mr. Trump, the crown may end up being a useful weapon in Britain’s campaign to keep the president-elect’s affections.

On Saturday, Mr. Trump forged ties to the next generation, meeting Prince William, the 42-year-old son of King Charles III, after both attended the reopening of Notre-Dame Cathedral in Paris. His comments afterward left little doubt that Mr. Trump savors his exposure to royals of any age.

“I had a great talk with the prince,” Mr. Trump told The New York Post. “He’s a good-looking guy,” the president-elect went on. “He looked really, very handsome last night. Some people look better in person? He looked great. He looked really nice, and I told him that.”