10 Saddest Doctor Who Companion Departures

Tennant and Tate were the dream team and the absolute pinnacle of New Who popularity. There's no doubt that season four was the best and a solid reason why fans are so excited for RTD to return.

Donna was the greatest companion because she played the best friend to the Time Lord and there was absolutely no romance between them; a relief after way too much in the previous seasons. She and the Doctor kept each other in check and just had great chemistry. It should have lasted forever.

Her exit was the most traumatic of all, though. In Journey's End, she became the "Doctor Donna" and had to have her memory wiped to save her life. Even when Ten caught up with her family later, he wasn't allowed to hang around because meeting her for too long could trigger the memories of their adventures and kill her. Seeing Donna's character development undone and her revert to an airhead gossip was painful.

It was at her wedding though, when Ten secretly attended and gifted her a lottery ticket that emotions were high all round. Obviously, we knew the ticket would be a winner and he was setting Donna up for a great start in her new life but she would never be able to know it was him, and that was just too much.