Complex sentence: In 1989, there were plans to unify All Star Promotions and Joint Promotions' British Heavyweight titles, pitting St. Clair against Dalbir Singh, but Singh joined All Star Promotions and renounced his claim to the title, making St. Clair the undisputed British Heavyweight Champion.
Split into simpler sentences: In 1989, there were plans to unify All Star and Joint's British Heavyweight titles, pitting St. Clair against Dalbir Singh. However, Singh would join All Star and renounce his claim to the title, making St. Clair the undisputed British Heavyweight Champion.