Queen dowager
Henry served as regent for his great-nephew King Sebastian, replacing his sister-in-law and Sebastian's grandmother Queen dowager Catherine, following her resignation from the role in 1562. King Sebastian died without an heir in the disastrous Battle of Alcácer Quibir that took place in 1578, and the elderly cardinal was proclaimed king soon after. Henry sought to be released from his ecclesiastical vows so he could take a bride and pursue the continuation of the Aviz dynasty, but Pope Gregory XIII, not wanting to antagonize Philip II of Spain, did not grant him that release.