Tennant was worried about working with Matt Smith on Doctor Who

David Tennant was worried working with Matt Smith on 'Doctor Who' would be a "weird situation".

The 42-year-old actor was concerned his decision to reprise his role as the Tenth Doctor on the BBC One sci-fi show's 50th anniversary episode would "backfire" because Matt replaced him as the titular Time Lord - but he was pleasantly surprised the pair worked together so well.