Complex sentence: Her affair with Mannox came to an end in 1538, when aged fifteen, Catherine moved and was pursued by a secretary of the Dowager Duchess's household in Lambeth, Francis Dereham.
Split into simpler sentences: Her affair with Mannox came to an end in 1538, when Catherine, now aged 15, moved to the Dowager Duchess's household in Lambeth. There she was pursued by a secretary of the Dowager Duchess Francis Dereham.