Complex sentence: Relations of Martina and her step-son were always difficult, so when Constantine III died suddenly of tuberculosis only four months later the common belief was that the Empress poisoned him to leave Heraclonas as sole ruler.
Split into simpler sentences: Relations of Martina and her step-son were always difficult. When Constantine III died suddenly of tuberculosis only four months later, the common belief was that the Empress poisoned him to leave Heraclonas as sole ruler.