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Genetic evidence has revealed the existence of a previously unknown human relative -- one ancient man must have had sex with.

According to Nature.com, a new analysis of the DNA footprint of Neanderthals and Denisovans -- a little understood group of ancient humanoids -- reveal the intense cross-breeding between different species tens of thousands of years ago. The study also unveiled the existence of an as-yet-unknown human ancestor that joined the party and likely cross-bred as well.

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“What it begins to suggest is that we’re looking at a ‘Lord of the Rings’-type world — that there were many hominid populations,” Mark Thomas, an evolutionary geneticist at University College London, told Nature.com.

Evolutionary geneticist David Reich presented the study at a Nov. 18 meeting of the Royal Society in London. He and a team of researchers presented a more complete genetic analysis of those ancient hominids than had previously been revealed, as well as bits of an extinct population that lived in Asia some 30,000 years ago.

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Who that group was is a complete mystery, experts said.

“We don’t have the faintest idea,” said Chris Stringer, a paleoanthropologist at the Natural History Museum in London, who was not involved in the work.

The group may be related to known offshoots of man -- literally kissing cousins, according to Carles Lalueza-Fox, a paleogenomics researcher at Pompeu Fabra University in Spain.

"It's implied it could be something like Homo erectus or similar," Fox, was who was present at the presentation, told LiveScience.