The Duke of Sussex smiled, waved and thanked an onlooker outside the Royal Courts of Justice in central London, where proceedings began in his case against the publisher of the Daily Mail, according to reports from The Mirror.
Dressed in a dark suit, white shirt and black tie, Harry is one of seven high-profile figures taking legal action against Associated Newspapers Limited. The claimants allege the publisher used unlawful methods, including hiring private investigators, accessing confidential information and intercepting phone calls.
Others involved in the case include Elton John and his husband David Furnish, campaigner Doreen Lawrence, former politician Simon Hughes, and actresses Sadie Frost and Liz Hurley.
Harry is expected to give evidence on Wednesday and Thursday but is not believed to be attending the remainder of the nine-week trial, which is being overseen by Mr Justice Nicklin.
Despite his return to the UK, reports suggest there will be no family meetings during the visit. Sources claim Harry will not see his father, King Charles, who is currently in Scotland and continuing cancer treatment. He is also not expected to meet with Prince William or Kate Middleton, despite earlier speculation about a possible reunion.
