The King has been seen beaming on his 77th birthday as he stepped out in South Wales alongside Queen Camila.
Their majesties are celebrating the day by meeting members of the local community at Cyfarthfa Castle near Merthyr Tydfil.
Charles officially opened the South Wales Metro Depot in Taff's Well, the heart of the South Wales Metro Project.
The King took to the driver's seat for a tram-train journey before meeting with Transport for Wales staff.
King Charles and Queen Camilla waved to crowds outside the castle
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Crowds applauded as the King and the Queen journeyed into the castle
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The Taff's Well Depot maintains 36 tram-trains, bringing together skilled mechanics, technicians, operational staff and cleaning crews.
Charles was welcomed by the First Minister of Wales before boarding one of the new tram-trains.
The vehicle His Majesty boarded is officially named Myddfai in reference to a small Carmarthenshire village near the monarch's former Welsh Home.
Over £1billion has been put into the project, being one of the most significant transport investments in Wales for a generation.
The King officially opened the South Wales Metro Depot
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King Charles spoke to members of the local community at Cyfarthfa Castle
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The King then toured the depot's facilities before having a group photo with Transport for Wales staff.
The reception at Cyfarthfa Castle featured guests from the local community as well as actress Ruth Jones, fashion designer Julien Macdonald and representatives from the Laura Ashley Foundation.
Individuals from the couple's patronages, including The King's Trust and the Royal Osteoporosis Society, and local businesses, were also in attendance.
The castle is celebrating its 200th anniversary with the reception, alongside His Majesty's birthday.
The King greeted well wishers in the pouring rain
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Hundreds of people gathered in the rain to greet the King and Queen
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Hundreds of people gathered in the rain, waiting to greet the King and Queen at the castle.
Charles also marked his 77th birthday with a new portrait from the Sandringham Estate.
Dressed in an open-necked shirt with a jacket and brogues while leaning gently on his shepherd's crook, the monarch posed for the picture by photographer Millie Pilkington.
The Royal Family wrote on Instagram: "77 today! Thank you for the kind words and well wishes on His Majesty's Birthday."
A 41-gun salute occurred at Green Park in Central London
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The Prince and Princess of Wales wished Charles a happy birthday on social media, saying: "Happy Birthday to His Majesty The King!"
Over 60,000 people have liked the King's portrait on Instagram, with hundreds of commenters wishing him a happy birthday.
A 41-gun salute occurred at Green Park in Central London to mark the King's birthday, one of many happening up and down the country.
Constitutional Expert Sir Michael Elis explained why it is a 41-gun salute.
He told GB News: "As head of state, as the King, he gets a 21-gun salute because heads of state get 21 guns, but because it is a royal park, he gets an extra 20."
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