Born on 8 February 1634 in Vila Viçosa, Teodósio was the first child of John IV of Portugal and Luisa de Guzmán, then the Duke and Duchess of Braganza.

[5] In 1646, John IV attempted to secure a dynastic alliance with France by proposing Teodósio marry Louis XIII's niece, La Grande Mademoiselle.

[6] Desperate to solidify the match, John secretly proposed abdicating his throne in favor of Teodósio.

[10] The focus on a humanist curriculum drew criticism from nobles who advocated for Teodósio's engagement in military service as befitting his role as crown prince.

[16] Teodósio's brother, the medically and mentally problem-ridden Afonso, succeeded him as Prince of Brazil, Duke of Braganza and heir apparent of the kingdom.