Complex sentence: The concert was in celebration of the fiftieth birthday of Hassanal Bolkiah, the Sultan of Brunei and was attended by some members the Brunei royal family, the Sultan himself did not attend however, due to official duties.
Split into simpler sentences: The concert was in celebration of the fiftieth birthday of Hassanal Bolkiah, the Sultan of Brunei. Some members the Brunei royal family attended, whilst the Sultan himself did not due to official duties.