The Royals

Prince William Takes Kate to Charity Event After All-Night Mission

By Simon Perry

09/29/2011 at 10:00 AM EDT

The Duchess and Duke of Cambridge

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Kate Middleton

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Prince William

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If Prince William looks a little weary at his royal charity event today with wife Kate, cut him some slack.

The prince, 29, was up all night flying emergency helicopter rescue missions over northwest Britain.

During a 24-hour shift that began at 10 a.m. Wednesday, Flight Lieutenant Wales (as William is known in the RAF) helped to fly a sailor from a Royal Navy ship off the Isle of Man 400 miles south to Sandhurst to see a sick relative. He also helped pick up a casualty with serious head injuries in the lake district.

He must have covered 1,000 miles during the shift. But on Thursday morning, he quickly headed to Surrey's Royal Marsden Hospital, of which he is president, where he met up with Kate, 29, to open a new children's cancer center.

"It was a bit of an early morning," he joked upon his arrival.

"If the Duchess is sprightlier than William, then that's the reason," a royal aide tells PEOPLE, referring to William's all-nighter.

The Marsden visit takes place as Kate starts to investigate what kinds of charities and causes she may adopt when she begins her public royal work.

Aides say that process is "going well."

But it's not all work. Kate has been spending time in London, where the couple have a home in the Kensington Palace compound, and has been stocking up on new fall fashions.