The King shared a sweet reference to his son, the Prince of Wales, as he and the Queen stepped out in Wales.
Charles, 75, delivered a speech to mark the 25th anniversary of the Senedd (Welsh Parliament) when he spoke of Prince William's growing relationship with the nation.
The King said: "It is a milestone on a journey which has been my privilege, all my life, to share with you – during times which have seen great change, profound sorrow, and tremendous achievement. Through it all, my respect and affection for the people of this ancient land have deepened with every passing year."
The former Prince of Wales added: "It has given me great pleasure to see my son's relationship with this special land continue, including returning only this week to Anglesey – Ynys Mon – a place which I know means so much to him.
"So, it is with countless special memories and particular pride that I am able to join you as we reflect upon the last quarter-century of the history we have shared, and which you – in your work in this Senedd – have the great responsibility of making."
Watch the King's speech in full here...
William, who became the Prince of Wales in September 2022, lived with his wife Kate on Anglesey as newlyweds when he served as an RAF search and rescue pilot at RAF Valley from 2010 to 2013.
The future king, 42, was reunited with his flying instructor during his nostalgic engagement on Tuesday.
It marked William's first visit to the base after he became Royal Honorary Air Commodore of RAF Valley last August after taking over the role from the King.
Marking a milestone
Charles returned to the Senedd for the first time since September 2022 following his accession and Queen Elizabeth II's death.
He and wife Camilla were greeted by a guard of honour from the Royal Welsh and a crowd of schoolchildren - see their arrival in the clip below...
The King donned a navy blue suit with a striped tie while the Queen looked pretty in a pale pink coat dress and a wide-brimmed raffia hat.
Inside the Senedd, the couple met party and parliamentary leaders and heard a performance by the King's new harpist, Mared Pugh-Evans, in her first performance in the position.
In 1999, the then National Assembly for Wales was established and many of the powers previously held by the UK Government were passed to Wales.
Now commonly known as the Senedd, the institution has undergone significant change, becoming a fully-fledged parliament with the ability to make laws in crucial areas.