As a result of the change in its status and the arrival of the Portuguese royal family, Brazilian administrative, civic, economical, military, educational, and scientific apparatus were expanded and highly modernized. Portuguese and their allied British troops fought against the French Invasion of Portugal and by 1815 the situation in Europe had cooled down sufficiently that João VI would have been able to return safely to Lisbon. However, the King of Portugal remained in Brazil until the Liberal Revolution of 1820, which started in Porto, demanded his return to Lisbon in 1821.

Answer this question, if possible (if impossible, reply "unanswerable"): Until when did the King of Portugal remain in Brazil?
until the Liberal Revolution of 1820