The answer lies in the marriage of Elizabeth Bowes-Lyon with Prince Albert, Duke of York, second son of King George V and Queen Mary, which took place on 26th April 1923. As Prince Albert held the title of Earl of Inverness, Baron Killarney, and Viscount Lascelles upon their marriage, the title in question is Viscount Lascelles.
Beyond the Royal Titles: Unraveling the Legacy of Mary, Princess Royal and Countess of Harewood