Theresa of Portugal (Portuguese: Teresa or Tereza, [tɨˈɾezɐ]; Archaic Portuguese: Tarasia; 1151 – 1218) was Countess of Flanders by marriage to Philip I, Count of Flanders, and Duchess of Burgundy by marriage to Odo III, Duke of Burgundy. She was the daughter of the Portuguese king Afonso I and Matilda of Savoy. She served as co-regent of Portugal with her brother during the illness of their father Afonso I of Portugal from 1172 until 1173, and regent of Flanders in 1191 during the interim period after the death of her spouse and the accession of his heir.
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Regent of Portugal
Theresa was the daughter of the Portuguese king Afonso I and Matilda of Savoy. Theresa, her brother Sancho, and sister Urraca were the only children of Afonso and Matilda to survive to adulthood. Named after her paternal grandmother, Countess Theresa, she was reputedly King Afonso I's favourite.
During their father's illness, Sancho at first exercised regency alone but from 1172 he shared the government with Theresa. At that time Afonso started considering to allow Theresa to succeed to the throne, and in 1173 he declared Sancho and Theresa co-heirs. As Afonso's illness progressed, the role of the siblings increased. Sancho took over military matters, while Theresa assumed administrative functions.
She was called queen because she was a regent of the kingdom of her father.