If fans were to pick the one scene that is the hardest to watch in “Doctor Who,” it would be the farewell scene between Donna Noble (Catherine Tate) and the Tenth Doctor (David Tennant) in Series 4. To set up the episode’s premise, Donna becomes the Doctor’s companion, gains the Time Lord DNA, and helps save the world.

Unfortunately, the transformation is too much and despite Donna’s protests, the Doctor is forced to erase her memories of their time together. In a Reddit thread, users cited this farewell as the saddest of the series with many saying they could heavily identify with Donna’s character.

Another user reflects on the Doctor’s tragic life, and how heartbreaking it is for him to lose Donna when she gave him the friendship that he so desperately needs. The Doctor comes to learn that “no matter what, he was going to lose people, because that’s part of life,” a sentiment that also resonated with the audience.