Complex sentence: It was also one of the last pieces he composed before illness forced him into retirement: the two piano concertos and the "Don Quichotte à Dulcinée" song cycle were the only compositions that followed "Boléro".
Split into simpler sentences: It was also one of the last pieces he composed before illness forced him into retirement. The two piano concertos and the "Don Quichotte à Dulcinée" song cycle were the only compositions that followed "Boléro".