From a royal bed and breakfast to lashings of public praise, everything possible had been done to keep Trump sweet, for fears he would blow up the carefully choreographed show of NATO unity.

It paid off.

Best of all for a leader who loves pomp and royalty, Dutch King Willem-Alexander rolled out the red carpet -- literally -- for Trump, hosting a gala dinner and inviting him for a sleepover, a last-minute change of plans.

Trump beamed as he met the Dutch king, queen and princess, later describing them as "beautiful and spectacular people."

"Central casting," he said of the Dutch royals, "Our breakfast meeting was great!"

Apparently refreshed by his regal breakfast, he lavished praise on the "beautiful Netherlands" as he rode in "The Beast" to the summit venue on Wednesday.

"I want to thank them for the royal treatment they've given us -- couldn't, couldn't have been nicer," he gushed.

"And it's a beautiful country... I saw the most beautiful trees. In fact, I want to bring some back with me."

His change in mood was reflected in a change of political tone.

While he had thrown a grenade into the summit while crossing the Atlantic on Tuesday by questioning NATO's one-for-all defence pledge, by Wednesday he was all smiles.

When he arrived, his hosts were full of praise.

"You were a man of strength, and you're also a man of peace," NATO Secretary General and so-called "Trump Whisperer" Mark Rutte told him.

As for Trump's four-letter outburst the day before -- as he berated Iran and Israel for violating a ceasefire deal -- Rutte was unfazed.

"Daddy has to sometimes use strong language," the NATO chief said.

- 'Your win' -

The cheery Trump who showed up at the summit was almost unrecognizable from the furious president who had left the White House less than 24 hours earlier.

Leaders gathering in The Hague were on edge as they watched Trump blast Israel and Iran as he feared a ceasefire he had just announced would crumble.

Even White House staffers were taken aback as Trump said the two countries "don't know what the fuck they're doing" -- perhaps the first time a sitting president has publicly cursed that way.

From Air Force One, the 79-year-old then unleashed a volley of more than a dozen furious social media messages on everything from domestic political rivals to NATO spending.

He seemed little happier when he spoke to reporters aboard the plane, saying that there were "numerous definitions" of NATO's core Article V collective defence treaty.

But one message showed the way to Trump's heart.

The president reposted a personal text from Rutte gushing that "Europe is going to pay in a BIG way" and that "it will be your win."

When he stepped off the plane on Tuesday evening, Trump already seemed in a better mood. He donned a white USA cap and smiled for the cameras at Amsterdam's Schiphol Airport.

- 'Big success' -

Trump's hosts then followed a well-worn path that Britain has also done in the past, knowing his reverence for Britain's Queen Elizabeth II.

The Dutch king welcomed Trump to dinner at the Huis ten Bosch palace in the woods outside the Hague, in a stunning blue baroque ballroom with frescos on the wall.

Trump, a property developer who has launched his own gilt-laden makeover of the White House, could be seen pointing at the ceiling in awe as he chatted to the monarch.

The next morning, a beaming Trump gave the thumbs up as he had breakfast with the king and his Argentinian wife.

For a man who has a habit of throwing international summits into turmoil and then leaving early, Trump also appeared in a good mood as he arrived at the summit.

Trump last year even suggested he would tell Russia to "do whatever the hell they want" with NATO members that didn't pay their way, but that all seemed forgotten.

"We're with them all the way," Trump said.

"I think the summit was fantastic. It was a big success," Trump told Dutch Prime Minister Dick Schoof.