Complex sentence: Her paternal grandparents were Thomas Holland, 1st Earl of Kent and Joan of Kent, mother of King Richard by her second marriage to Edward, the Black Prince, and her maternal grandparents were Richard Fitzalan, 10th Earl of Arundel and Eleanor of Lancaster.
Split into simpler sentences: Her paternal grandparents were Thomas Holland, 1st Earl of Kent and Joan of Kent, mother of King Richard by her second marriage to Edward, the Black Prince. Her maternal grandparents were Richard Fitzalan, 10th Earl of Arundel and Eleanor of Lancaster.