 Brocas was the son of Sir John Brocas of Clewer in Berkshire, a Master of the King's Horse.He grew up with the Black Prince at Windsor Castle, at a time of rebuilding by the Royal architect William of Wykeham.After a scandalous first marriage, to Agnes, daughter of Mauger Vavasour of Yorkshire, which ended in divorce, the Prince intended Brocas to marry his cousin, Joan, the Fair Maid of Kent but when Joan said she loved Edward, he decided to marry her himself.