3. Death of the Brig (The Wedding of River Song, 2011)
As the Doctor prepared for battle, he was flying high, convinced nothing could stop him. Then he placed a call to his friend, Brigadier Sir Alistair Gordon Lethbridge-Stewart, and found out that the old soldier had died. It was a great recognition of the passing of Nicholas Courtney, who had played the role, but it was also a heartbreaking moment for the audience and a wonderful way to slap the Doctor back to reality.