"Human error in cloudy weather" led to the chopper crash that killed India's first military chief General Bipin Rawat, his wife, and 12 other armed forces personnel last month, a tri-services probe has concluded. According to the probe report, a sudden cloud cover over Coonoor district in the hilly terrain of the Nilgiris in the southern state of Tamil Nadu led to the military chopper's "unintentional collision with a mountain" on December 8. Head of the Indian Air Force Air Chief Marshal Vivek Ram Chaudhari shared the tri-services probe report with Defence Minister Rajnath Singh on Wednesday. READ: Sole survivor of Indian military chief's chopper crash dies  Tri-services probe means an investigation by the three branches of the military -- the Indian Army, the Navy, and the Air Force. The 63-year-old Chief of Defence Staff was on his way to deliver a lecture at Defence Services Staff College in Wellington when the Mi-17 V5 chopper crashed in the Nilgiris and burst into flames. "With deep regret, it has now been ascertained that Gen Bipin Rawat, Mrs Madhulika Rawat (wife) and 11 other persons on board have died in the unfortunate accident," the Air Force tweeted. Another victim, a senior Air Force, official died later. Moments later, Indian President Ram Nath Kovind, the supreme commander of the armed forces, tweeted to say that "the nation has lost one of its bravest sons". Prime Minister Narendra Modi, on his part, had described the four-star General as "an outstanding soldier". READ: India orders tri-services probe into military chief's chopper crash General Rawat has had a chequered career in the armed forces spanning over 40 years, rising from the rank of a junior commissioned officer to the Indian Army chief and eventually the first head of the tri-services. He reported directly to the Indian Prime Minister.