Catherine Seymour, Countess of Hertford, was born at Bradgate Park in Leicester, on the 25th of August, 1540.
She was the second surviving daughter of Henry Grey, 1st Duke of Suffolk, by his marriage to Lady Frances Brandon. She was the younger sister of Lady Jane Grey and older sister of Lady Mary Grey. Catherine Grey’s maternal grandparents were Charles Brandon, 1st Duke of Suffolk and Mary Tudor, younger daughter of Henry VII.
During the first phase of Mary I’s reign, she was a potential successor to the throne as Mary was unmarried and Elizabeth was considered Illegitimate, however, when Elizabeth was declared heir, she was demoted.