After the Doctor held Donna’s unconscious form, when he took everything he had ever done with her away. He held her for the briefest moment:

"I died for you, Donna. Please don’t mourn me."

For some reason, whenever her grandfather invited her to look at the stars, she had the most sincerest feeling of longing. As if something in the sky was missing…sometimes, she had the strangest notion that it was her…