An aircraft seat assembly structure (4) comprises at least one seat structure (5) that supports at least one seat, with which seat assembly structure is associated a reference frame that is defined by a longitudinal X-axis according to which the seat structure (5) comprises a front part and a rear part, by a Y-axis that is perpendicular to the X-axis, and that forms with said X-axis a horizontal XY plane when at least one seat is horizontal, and by a Z-axis that is perpendicular to the XY plane. In the front part, the seat structure (5) comprises a torsion bar (50) that is essentially parallel to the Y-axis that is equipped at a first lateral end (502) with a front lateral fastening device (500) that is designed to be made integral with lateral attachment means (26) of a shell structure (2) of an aircraft. The invention also relates to a fuselage that comprises said shell structure that is equipped with said lateral attachment means, whereby the aircraft comprises said fuselage and the seat assembly structure (4).