Complex sentence: Sophia died on 8 June 1714, before the death of Queen Anne on 1 August 1714, at which time Sophia's son duly became King George I and started the Hanoverian dynasty.
Split into simpler sentences: Sophia died on 8 June 1714, before the death of Queen Anne on 1 August 1714. On Queen Anne's death, Sophia's son duly became King George I and started the Hanoverian dynasty.