NEW DELHI, Dec 15 (Reuters) - The only survivor of last week"s helicopter crash that killed Indian defence chief General Bipin Rawat and 12 aboard succumbed to his injuries on Wednesday, the air force said. Group Captain Varun Singh was among the 14 people travelling in the Indian Air Force (IAF) helicopter that burst into flames after ploughing into a hillside in the southern state of Tamil Nadu. read more Thirteen were declared dead soon after, including Rawat and his wife, but Singh survived and was placed on life support. "The IAF offers sincere condolences and stands firmly with the bereaved family," it said on Twitter. Indian Defence Minister Rajnath Singh expressed sorrow at the death, adding, "He was a true fighter who fought till his last breath." Singh was serving at the Defence Services Staff College in the cantonment town of Wellington, to which Rawat and his entourage were being ferried in the Russian-designed Mi-17 chopper that crashed around noon amid heavy fog. As India"s first chief of defence staff, Rawat, 63, led one of the world"s largest armed forces. The Indian Air Force has ordered an inquiry into the accident.