Complex sentence: In 1487, after Henry VII's accession and marriage to her sister Elizabeth, Cecily was married to John Welles, 1st Viscount Welles, the son of Lionel Welles, 6th Lord Welles and Margaret Beauchamp of Bletso.
Split into simpler sentences: In 1487, after Henry VII's accession and marriage to her sister Elizabeth, Cecily was married to John Welles, 1st Viscount Welles. Her new husband was son of Lionel Welles, 6th Lord Welles and Margaret Beauchamp of Bletso.