Serena, Marchioness of Bute—or Lady Bute, if we’re being formal—was already seated by the fire in the Ladder Shed bar of London’s Chiltern Firehouse. The languid blonde with long legs and electric blue eyes looked up, smiling shyly.

We’d come to discuss her eponymous range of silk track pants and matching shirts, popular with fashionistas. Its sales have grown exponentially since the line’s launch, in 2015. Bute was wearing an outfit from her latest drop: a relaxed-fit, light-blue, hammered-silk shirt and white pajama-like trousers, with a white blazer.