Last updated 28 March 2020
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Alex Klein was the senior aide to Harriet Jones in Downing Street in 2006. He was with her when she was teleported aboard the Sycorax ship. He acted as a translator until the TARDIS resumed its translation. Her premiership crumbled when the Tenth Doctor whispered to Alex, "Don't you think she looks tired?" — six words that began a chain of events leading to her downfall.
Biography from the TARDIS Data Core article, licensed under CC-BY-SA