As per tradition, the King has acknowledged the century celebrations of people in the Commonwealth.
Ruth Park-Pearson was one of the first to receive a card from the King and Queen Consort Camilla.
Mrs Park-Pearson served in the Women's Royal Naval Service under George VI, the Queen's father, and reflected how Charles III was the fifth monarch of her lifetime.
"You don't think about it at the time, it's not until later you realise just sort of how old you are suddenly. You think my goodness me, I remember the old King," she told the BBC.
The Palace suspended the centenary birthday cards during Queen Elizabeth II's mourning period.
The new cards styled for King Charles and Queen Consort Camilla then had to be designed and printed.
The cards feature a photo of the couple on the front, taken in the summer of 2018.
Cards are sent out by the Palace on 100th and 105th birthdays, as well as to celebrate couples' 60th, 65th and 70th wedding anniversaries.
