William became aware of HIV/AIDS in the mid-1990s when he accompanied his mother and brother on visits to shelters and clinics for patients. In January 2005, William and his brother volunteered at a British Red Cross aid distribution centre to pack emergency supplies for countries affected by the 2004 Boxing Day tsunami. In September that year, William granted his patronage to Centrepoint, a charity that assists the homeless. In December 2009, he, as part of a Centrepoint-organised event, spent the night sleeping bag near the Blackfriars Bridge to raise awareness of the experiences of homeless youth. The Duke opened their new facility, Apprenticeship House, in November 2019 to mark their 50-year anniversary. In 2005, William worked in the children's unit at The Royal Marsden Hospital, his mother's former patronage, for two days of work experience; he also assisted in the medical research, catering, and fundraising departments. In May that year, he spent two weeks in North Wales with Mountain Rescue England and Wales. In May 2007, William became patron of both organisations. In October 2020, the Duke laid the foundation stone of the hospital's Oak Cancer Centre, 30 years after his mother did the same for their Chelsea Wing in 1990.