King Charles parried questions about the arrest of his brother, Andrew Mountbatten-Windsor after he arrived to attend a fashion show in London on Thursday.
The monarch attended the show hours after issuing a statement on the former Duke of York's arrest, saying "The law must take its course."
Commenting on pictures and videos from the show, social media users said the king looked unbothered by his brother's arrest.
Some said the younger brother of King Charles III deserved to be detained and others that it sent the right message that the royal family is not above the law.
Andrew Mountbatten-Windsor, as he is now known, was detained on suspicion of misconduct while acting as a UK trade envoy.
According to Reuters news agency, the king appeared at a fashion show in London on Thursday just hours after his brother Andrew Mountbatten-Windsor was arrested on suspicion of misconduct in public office.
Charles greeted onlookers with a wave when he arrived at Tolu Coker's London Fashion Week show and was met with applause inside the room.
Watching the British-Nigerian designer's collection he chatted animatedly to British Fashion Council Chief Laura Weir and designer Stella McCartney on the front row.
Earlier on Thursday, Mountbatten-Windsor was arrested by police and detained in custody to be questioned over allegations he sent confidential government documents to Jeffrey Epstein.
The arrest of the senior royal, eighth in line to the throne, is unprecedented in modern times and presents Charles with the biggest crisis of his reign.
The king issued a statement expressing his "deepest concern" about the news. "Let me state clearly: the law must take its course," he said.
"Meanwhile, my family and I will continue in our duty and service to you all."
Charles' visit to London Fashion Week, which was planned in advance, combined his eye for classic British style with his support for traditional crafts.
The monarch, a long-time customer at London's famed Savile Row street of tailors, watched as models presented the latest creations by Coker, who is known for celebrating cultural identity and craftsmanship in her work.
Charles, 77, follows in his late mother's footsteps by attending a London Fashion Week show. In 2018, Queen Elizabeth sat beside fashion editor Anna Wintour on the front row at Richard Quinn's show.
Coker, who launched her eponymous brand in 2021, was showing as part of the British Fashion Council's NEWGEN programme, which provides financial support and mentoring for new designers.
Before the show, Charles toured exhibitions at the London Fashion Week hub, including one by designer McCartney, known f for using alternatives to leather and fur in her designs, focusing on sustainable British innovation.