- Brother of Sancho II of Portugal, whom he succeeded, after a short period of regency between his brother's removal from the throne and his death in 1248.
- Also known as Count of Boulogne, as he was married to the Matilde II, Countess of Boulogne in her own right (c.1238). [Fernando, ch. 81: 19-21]
- In 1253, Afonso III repudiated Matilde of Boulogne to marry Beatriz of Castile, illegitimate daughter of Alfonso X, the Wise, of Castile.