Vladimir Putin "has added two investigative journalists to a Kremlin kill list" after their explosive new biography alleged the Russian president groomed a teenage model and that his late father was even more unhinged than him, security sources tell RadarOnline.com .

Insiders say research carried out by Roman Badanin, 46, and Mikhail Rubin, 42, co-authors of The Tsar in Person: How Vladimir Putin Fooled Us All , has triggered direct threats from Moscow. Article continues below advertisement

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It led to them publishing lurid details of Putin's private life and his family history in their newly-released tome.

The book alleges Putin had a secret relationship with 17-y

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