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The actress will appear alongside returning guest star James Corden, according to Wales on Sunday.
Baron's recent television credits include her role as Linda Clarke on Eastenders and guest appearances in Marple and Casualty.
She has also made two previous contributions to Doctor Who, appearing in the 1983 story 'Enlightenment' as Captain Wrack, and performing a song for the 1966 serial 'The Gunfighters'.
Her new role has yet to be officially confirmed by the BBC.
Doctor Who will return to BBC One later in the spring.
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