Complex sentence: Evelyn was married on 30 July 1892 to Victor Cavendish, who succeeded his uncle as 9th Duke of Devonshire in 1908, whereupon Evelyn became Duchess of Devonshire.
Split into simpler sentences: Evelyn was married on 30 July 1892 to Lord Victor Cavendish. Victor succeeded his uncle as 9th Duke of Devonshire in 1908, whereupon Evelyn became Duchess of Devonshire.