An Airbus 330-343 aircraft, operating as Air Canada 875, with 253 passengers and 13 crew members on board, was on a scheduled flight from Frankfurt, Germany, to Montreal, Quebec. As the aircraft was taking off at approximately 0830 Coordinated Universal Time on Runway 25R, the underside of the tail struck the runway. The strike was undetected by the flight crew, but they were notified of the strike during the climb-out by Air Traffic Services (ATS) and by a cabin crew member. The flight crew requested a holding pattern to assess the situation. After discussion with the company, the flight crew decided to return to Frankfurt. ATS vectored the aircraft for an instrument landing system (ILS) approach to Runway 25R. While established at 4000 feet above sea level (asl), on the localizer, at about 17 nautical miles (nm) from the threshold, with the autopilot engaged, the aircraft pitched up to 26.7 degrees. The autopilot was disconnected and control of the aircraft was recovered. The approach was completed manually, and an uneventful overweight landing was carried out on Runway 25R. The aircraft sustained substantial structural damage to the underside of the tail as a result of the tail strike. There was no requirement for an evacuation, and there were no injuries.