Since we're all guessing, try this.
Aircraft lands in water in a slight right bank. Starboard engine/wing take much of the impact, engine drops off, the sudden yank to starboard cracks the hull aft of the wing.
The aircraft groundloops (sealoops?) around the starboard wing, coming to rest very suddenly after doing a 270 to its original direction. Sudden stop serves to complete tail section fracture/separation.