The state visit also showed the scope of the “soft power” that the royal family has.

“It was really uplifting. It showed what we can really do when we push out the stops. Despite everything that’s going on in the world, we are still the best at putting on a show of pomp and circumstance,” says Seward. “Years ago, Charles said we must never lose that because that is what we do best — and he is absolutely right.”

After the King, 76, and Queen, 77, bid farewell to Trump, 79, and Melania, 55, on Sept. 18, Princess Kate stepped back into the spotlight by undertaking her first joint appearance with the American first lady.

The Princess of Wales and Melania visited a group of young children involved in the U.K’s Scouts Squirrels program, connecting to Kate’s role as joint president of the Scouts, an outing at which the first lady smiled throughout.

Princess Kate and Melania have both made children’s causes a focus of their public work, and they seemed to be at ease in one another’s company.

“She chatted to Kate quite a lot. Everybody wants to talk to Kate,” the royal author says about their rapport on display that day.

As to whether the Princess of Wales is the royal family’s “secret weapon,” Seward says it’s simple: “She is the weapon, not a secret one,” emphasizes the author of several books on the late Queen Elizabeth.