Complex sentence: When the duke died in 1758, she became engaged to the Duke of Bridgwater but the engagement was cancelled that year for reasons unknown, and on 3 February the following year she married John Campbell, Marquess of Lorne.
Split into simpler sentences: When the duke died in 1758, she became engaged to the Duke of Bridgwater but the engagement was cancelled that year for reasons unknown. On 3 February the following year she married John Campbell, Marquess of Lorne.