Complex sentence: However, four years later he became Prince Regent because of Queen Maria I's mental illness, and in 1816, he became King John VI, after the Queen's death while the Royal Family was residing in Rio de Janeiro.
Split into simpler sentences: However, four years later he became Prince Regent because of Queen Maria I's mental illness. In 1816, John VI became King after Maria I died while the Royal Family was residing in Rio de Janeiro.