Complex sentence: The previous season they had finished as runners-up in the same three competitons, this to date is the only occasion that a club has completed a runner-up treble and a winners treble in consecutive seasons.
Split into simpler sentences: The previous season they had finished as runners-up in the same three competitons. This to date is the only occasion that a club has completed a runners-up treble and a winners treble in consecutive seasons.