Complex sentence: Makhosetive was crowned Mswati III, Ingwenyama and King of Swaziland on April 25,1986 at the age of 18, thus becoming the youngest ruling monarch at the time in the world.
Split into simpler sentences: Makhosetive was crowned Mswati III, Ingwenyama and King of Swaziland on April 25,1986 at the age of 18. He thus became the youngest ruling monarch at the time in the world.