He spoke Tuesday of the "splendid" news that his daughter-in-law Kate is expecting her second child.
Charles, 65, was greeted by well-wishers at a charity event in London and spoke of how "wonderful" it will be to become a grandfather again.
Kate and husband William announced the pregnancy Monday – weeks ahead of when they planned to – because she was forced to cancel a public appearance due to severe morning sickness.
Kate suffered from the same illness, Hyperemesis Gravidarum, when she was carrying Prince George, now 13 months.
With the sensitivity of her situation in mind, it was thought Charles would not say anything about the news.
But when those gathered at a Prince's Trust project in South London asked him about it, he was happy to chat.
Toying Owoseje, 26, told reporters she offered her congratulations when she shook his hand. Charles quipped, "What did I do?" before adding, "It's not here yet!"
Then, the prince said, "No, it's wonderful. We are very happy. It's splendid, very exciting."
Owoseje was introduced to Charles by her sister, Damilola, who set up an furniture design business with the help of Charles's charity.