The Prince of Wales received get well soon cards for his wife on his first official engagement since the Princess of Wales's cancer diagnosis.
He appeared moved as charity volunteer Rachel Candappa handed him the cards.
When Mrs Candappa, 71, asked him about Catherine, telling him to "take care of her", William replied: "I will."
The prince had taken a step back from royal appearances to spend time with the princess and his three children.
William helped volunteers prepare food deliveries on a visit to Surplus to Supper in Sunbury-on-Thames, Surrey on Thursday.
His most recent royal duty was a visit to a homelessness project in Sheffield in March, days before the Catherine released a video statement announcing she was in the early stages of cancer.
Although he has not made any official engagements since then, he has been seen in public.
As part of Thursday's visit to Surplus to Supper, the prince tried his hand at meal prepping in the charity's kitchen, and was seen stirring away at a bubbling pot and cutting celery.
Image source, Getty Images
Image source, Getty ImagesAfter helping load food deliveries into the charity's vans, Prince William joined volunteers, ready to visit a youth centre that receives the charity's aid in Feltham, west London.
Last week, the prince was seen with his eldest son Prince George at an Aston Villa football match.
Catherine has not attended any official events since Christmas.
In a shock announcement in March, the Princess of Wales revealed her cancer diagnosis, after weeks of speculation on her whereabouts.
Her cancer was discovered in post-operative tests following her abdominal surgery in January.
The princess won't return to royal duties until she is cleared by her medical team, but there is no timeline for this.
She has not been seen or heard from in public since her announcement, aside from a joint statement with William on X/Twitter last week, paying tribute to the victims of the Sydney attacks.