Regret

Choosing to leave her behind in 22nd century England, the First Doctor told Susan Foreman to go forward without regrets, tears or anxieties. (TV: The Dalek Invasion of Earth)

After departing from a giant toyshop which contained an interdimensional doll's house, the Second Doctor was left with a sense of regret that he could never understand. (PROSE: The Celestial Toyshop)

Constance Clarke received a telegram telling her that the Royal Navy regretted to inform her of Lt-Cmdr Henry Clarke's disappearance. (AUDIO: Quicksilver)