Read full story
He hadn't slept for more than 24 hours having just completed search and rescue duty with the RAF.
But that didn't stop Prince William looking cheery as he attended the opening of a new children's cancer unit at the Royal Marsden Hospital.
Having just met up with his wife, the Duchess of Cambridge in London after two overnight call-outs, the kind-hearted royal arrived with his new bride on Thursday afternoon.
The royal couple were warmly welcomed by members of staff and the public, many of whom had brought along banners.
On only her second UK charity engagement, Kate looked relaxed and typically elegant in a form-fitting grey dress.
The Royal Marsden holds a special place in William's heart.
He has been the cancer hospital's president since May 2007 – a position previously held by his mother Diana.
More on William and Kate