Complex sentence: In 1961 he was bestowed as the "Pengiran Muda Mahkota" ("Crown Prince") and subsequently as the Sultan of Brunei Darussalam on 4 October 1967, after his father had abdicated voluntarily.
Split into simpler sentences: In 1961 he was bestowed as the "Pengiran Muda Mahkota" ("Crown Prince"). His Highness subsequently become the Sultan of Brunei Darussalam on 4 October 1967, after his father had abdicated voluntarily.