A split rear backrest is arranged between two side panels of a motor vehicle and has two backrests, which are provided with respective lower portions arranged side by side along a horizontal axis and are rotatable independently of each other about said horizontal axis; moreover, the backrest has a shaft, whose ends define respective fastening elements for being coupled to the side panels; the shaft has a segment axially protruding from one of the backrests and rotationally engaging a seat axially formed in the other backrest.