Complex sentence: By the age of three he was living in Warminster, a town west of London, in his paternal grandparents' home and under the care of his aunt, Millicent "Cissie" Bartholomew, who raised him and became his stepmother.
Split into simpler sentences: By the age of three he was living in Warminster, a town west of London, in his paternal grandparents' home. He lived under the care of his aunt, Millicent "Cissie" Bartholomew, who raised him and became his stepmother.