Complex sentence: It was Montreal's first trip to the finals in four years when they lost to the Calgary Flames, in-province rivals of the Oilers, while it was the first-ever trip to the finals for the Kings in their 26-year history.
Split into simpler sentences: It was Montreal's first trip to the Finals since 1989, when they lost to the Oilers' provincial rivals, the Calgary Flames. Meanwhile, it was the first-ever trip to the Finals for the Kings in their 26-year history.