Complex sentence: Despite its hatchback shape, the car is a fastback and has a classic trunk (and a unique to the C6 concave rear window) such as the one its ancestor the Citroën CX used to have.
Split into simpler sentences: Despite its hatchback shape, the car is a fastback. It has a classic trunk and a unique to the C6 concave rear window such as the one its ancestor the Citroën CX used to have.