The King has some rather unusual advice as he met a 101-year-old war veteran during a visit to Lancashire on Monday.
Charles, 76, who is also known as the Duke of Lancaster, took part in a ceremony of keys outside Lancaster castle, a tradition which dates back to 1851 when the keys were presented to Queen Victoria.
At a reception at the castle, the monarch met Richard Brock, who served in the D-Day landings, remembered him from a visit to Normandy last year.
After asking Mr Brock's age, the King said: "You are fantastic."
As he left, he quipped: "Keep drinking the whisky."
Mr Brock, who served with the East Lancashire Regiment, later said: "He just told me I was amazing for my age."
His son Tony Brock, who attended the reception with him, said: "He mentioned a nip of whisky and said to keep taking it."
Welcome to Lancaster
Despite a group of Anti-monarchy protestors chanting, 'Not my King' outside the castle, crowds of well-wishers had gathered to greet the King, some of whom had been waiting since 5am.
Among those keen to see Charles were friends Joan Hardcastle, 103, and Barbara Graham, 93, who had come with staff and two other residents from Laurel Bank Care Home.
Mrs Hardcastle held a framed photograph of Charles presenting her with her MBE for voluntary services 40 years ago.
She said: "I’ve seen him several times since. He was fine when I met him, very chatty."
Care home manager Lyndsay Scott said: "It was Barbara's idea to come. We got here at 9am, we've had flasks of tea and croissants."
After taking part in the ceremony and inspecting a guard of honour, the King then met local business owners who were showcasing their work inside the grounds.
Family outing
The King paid an unannounced visit to the Royal Windsor Flower Show at Windsor Great Park alongside his sister-in-law, the Duchess of Edinburgh, on Saturday.
Charles, who has a passion for gardening, stopped to smell the flowers during his visit to the show which is billed as "a joyful one-day celebration of gardening, nature, food and traditional crafts".
Gardener Alan Titchmarsh, who is the honorary president of the Royal Windsor Rose & Horticultural Society, helped to welcome the royal party including the Duchess of Edinburgh who officially opened the event.
Charles and Sophie were seen warmly greeting one another as they arrived at the event, with the Duchess almost losing a shoe as she curtsied to the King.