John Bacon

USA TODAY

King Willem-Alexander of the Netherlands hasn't been resting on his monarchical laurels, telling Dutch media he has been moonlighting as a copilot for a KLM airlines affiliate for more than two decades.

The king told Holland's Telegraaf newspaper he co-pilots two KLM Cityhopper flights per month. And now he is training to fly with the big boys, Boeing 737s for KLM itself — coincidentally known as Dutch Royal Airlines.

"You can completely switch off and focus on something else," he told the Telegraaf. He said it is impossible to fly a plane if you bring "problems from the ground with you."

Willem-Alexander, 50, said he often walks through Amsterdam Airport Schiphol in his pilot uniform without being recognized by his subjects. He said that, before the Sept. 11 terror attacks, cockpit doors were often open and some people peeking in "found it fun or amazing to see me" at the controls.

"After September 11th, the cockpit door is closed and there is much less contact between the cabin and the cockpit," he said. "But yes, some people recognize my voice during the flight."

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Willem-Alexander, who ascended to the throne following his mother's abdication four years ago, said he often won't say his name while making flight announcements, preferring to welcome passengers on behalf of the captain and crew.

"Then I don't have to say my own name — but most people don't listen in any case," he said.

KLM pilot Maarten Putman, who regularly flies with the King, told the Telegraaf that Willem-Alexander is an excellent co-pilot.

"For the relatively few flying hours the king makes, he is always very sharp," Putman told the Telegraaf. "He knows the procedures well."

Willem-Alexander's side job is not unprecedented. England's Prince Charles is a retired Royal Air Force pilot, and his sons William and Harry flew military helicopters.