In a video message last month, Kate, 42, the Princess of Wales, said tests taken following major abdominal surgery she underwent in January had uncovered cancer, something she described as a "huge shock".
William, 41, has been absent from official engagements since then as the couple and their three young children come to terms with the effect of the news.
Although he and his eldest son Prince George were pictured watching their favourite football team Aston Villa play last week, Thursday marked the first time William carried out official public appearances since Kate's highly-personal announcement.
He appeared in good spirits as he chatted and helped out staff on a visit to a surplus food redistribution charity.
One volunteer handed him "get well soon" cards for Kate and his father King Charles who is also undergoing treatment for an unspecified form of cancer.
"Oh, you're very kind. Thank you very much," the prince said to her.
He later visited a youth centre which received regular deliveries from the charity.
Kate, often referred to by her maiden name Kate Middleton, will return to public duties herself when her medical team say she is well enough to do so, her office has said, but no timescale has been put on this.
Her illness comes at the same time as the King has been absent from public duties since his diagnosis.
However, he did greet crowds during a walkabout after an Easter church service at the end of March.
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