Adam Lambert is backing Alisan Porter to win this year's The Voice US series.

The singer took to Twitter overnight to pledge his support for his friend.

Calling her a "beast", the US star told fans to vote for Porter - who is a former child star - in the play-offs section of the show.

Lambert is well accustomed to TV talent shows, having found fame on American Idol in 2009.

The singer finished runner-up to eventual winner Kris Allen.

The vocal powerhouse has since returned to Idol every year as a performer or mentor.

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Watch Alisan Porter in action below: