Complex sentence: Three years later, in 1842, the regiment escorted Queen Victoria during her tour of Perthshire and, in 1844, when the Queen stayed as a guest of the Duke at Blair Castle, the regiment mounted the guard for the entire duration of her stay.
Split into simpler sentences: Three years later, in 1842, the regiment escorted Queen Victoria during her tour of Perthshire. In 1844, when the Queen stayed as a guest of the Duke at Blair Castle, the regiment mounted the guard for the entire duration of her stay.