Douglas and his company joined Alfonso's army, which then was setting out for the frontier of Granada to besiege the castle of Teba. Uthman ibn Abi al-Ula, the Berber general in command of the Moorish forces, marched to relieve the border stronghold. At some point during the siege, Douglas was killed. Sources and commentators differ as to how. According to Jean Froissart and the "Gran Cronica de Alfonso XI", Douglas was killed as a result of making a premature attack on the enemy. The "Gran Cronica" suggests this might have been during fighting for access to water. Citing John Barbour, some modern commentators believe he died in the decisive Battle of Teba. Barbour describes a grand battle in Spain but the setting is vague and the outcome ambiguous.