What are these emoluments you speak of?

The general manager of the Trump International Hotel in Manhattan had a rare bit of good news to report to investors this spring: After two years of decline, revenue from room rentals went up 13 percent in the first three months of 2018.

What caused the uptick at President Trump’s flagship hotel in New York? One major factor: “a last-minute visit to New York by the Crown Prince of Saudi Arabia,” wrote general manager Prince A. Sanders in a May 15 letter, which was obtained by The Washington Post.

Neither Crown Prince Mohammed bin Salman nor members of the royal family stayed at Trump’s hotel, Sanders said: He said the Trump hotel didn’t have suites big enough to accommodate them. But “due to our close industry relationships,” he wrote, “we were able to accommodate many of the accompanying travelers.”

The previously unreported letter — describing a five-day stay in March that was enough to boost the hotel’s revenue for the entire quarter — shows how little is known about the business that the president’s company does with foreign officials.

Such transactions have fueled criticism that Trump is reaping revenue from foreign governments, even as he controls U.S. foreign policy toward those countries. Trump’s company has disclosed few details about the business it does with foreign customers, saying it already reveals more than is required.

Neither the Trump Organization nor the Saudi Embassy answered questions about whether the Saudi government paid for anyone’s stay at the hotel. Sanders did not respond to requests for comment.

For now, just a handful of foreign government clients at Trump properties have been publicly identified through media reports and statements from foreign officials.

But a broader list could eventually come out.

Last week, a federal judge in Maryland gave the go-ahead to a lawsuit alleging that by accepting government business at his properties, Trump is violating the Constitution’s “emoluments clauses” — dusty 18th-century measures meant to prevent presidents from putting their private bank accounts ahead of the public interest.

If it stands, the ruling could force the company to provide new details about its relationships with foreign governments, states and even federal agencies.