The 70t titanosaur, which at 37m from nose to tail is nearly the length of four London buses, was discovered by a Patagonian shepherd, who found the tip of a giant thigh bone in the Argentinian province of Chubut in 2014.
The femur was 2.4m long, the largest that has ever been found.
Palaeontologists later discovered more than 220 fossilised bones, belonging to seven separate dinosaurs, one of which is thought to be the biggest creature ever to walk the earth.
The number of bones allowed experts to assess its weight, estimated at 70t.
Some of the bones weighed more than half a metric ton, so were hard to move from their remote location.
Analysis of the leg bones shows that these vast titanosaurs were young adults in their prime but were still growing. So we now know that a fully grown specimen would have been even bigger.
Evidence shows that all of the bones belonged to a new species. The name of this new species will be announced soon when the scientific paper is published.
Diego Pol, lead scientist on the excavation based at the Museum of Palaeontology Egidio Fereuglio, in Trelew, Argentina, said: “It was like a palaeontological crime scene, a unique thing that you don’t find anywhere else in the world, with the potential of discovering all kinds of new facts about titanosaurs.
“According to our estimates this animal weighed 70t. A comparison of the back bones shows it was 10% larger than Argentinosaurus, the previous record holder. So we have discovered the largest dinosaur ever known.”
Filmed over two years, Attenborough and the Giant Dinosaur, which will air on BBC One on January 24, follows the scientists’ forensic investigations, as they seek to prove the dinosaur is the largest ever to be discovered.