Sir John Key has revealed he helped Prince William slip his security detail during a trip to New Zealand in 2011.
The prince visited New Zealand in March 2011 just before his wedding to attend memorials for the Pike River Mine disaster and Canterbury earthquake.
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Sir John told Daily Mail columnist and royal biographer Robert Harding he helped William sneak away from his guards while they were on the West Coast, NZME reports.
The pair had been housed in rooms next to each other whilst on the trip.
"In the morning, I was writing my speech on my balcony and he said to me from his balcony: 'Do you think I could go for a walk on my own?'" Sir John said.
"I said: 'Go that way.' And he climbed down and off he went. That's the nice thing about New Zealand - you could do that."
Sir John told NZME William's security never found out about the secret walk.
The former Prime Minister also opened up about his other experiences with royalty, including a personal conversation with Queen Elizabeth II.
He asked why she always wore formal wear, even in private.
"I am the last bastion of standards," she replied.