Henry claimed that this lack of a male heir was because his marriage was "blighted in the eyes of God". Catherine had been his late brother's wife, and it was therefore against biblical teachings for Henry to have married her (Leviticus 20:21); a special dispensation from Pope Julius II had been needed to allow the wedding in the first place. Henry argued the marriage was never valid because the biblical prohibition was part of unbreakable divine law, and even popes could not dispense with it. In 1527, Henry asked Pope Clement VII to annul the marriage, but the Pope refused. According to canon law, the pope could not annul a marriage on the basis of a canonical impediment previously dispensed. Clement also feared the wrath of Catherine's nephew, Holy Roman Emperor Charles V, whose troops earlier that year had sacked Rome and briefly taken the Pope prisoner.