Princess Margaret's ex-husband Antony Armstrong-Jones' mistress Melanie Cable-Alexander has opened up about her relationship with Lord Snowdon, which took place during his second marriage.

Queen Elizabeth II's sister married photographer Antony at Westminster Abbey on 6 May 1960, two months after they announced their surprise engagement. Following an eighteen-year marriage, during which time they welcomed two children Lady Sarah Chatto and David Armstrong-Jones, they split in 1978 and made history as the first royals to divorce since King Henry VIII in 1540.