Estelle Cole was a woman who had known Jack Harkness during the War. She first met him at the Astoria Ballroom. When she met Jack again in the 21st century, she believed he was the son of the Jack she had known. Jack loved her when she was young and old. They made a vow that they would be together till they died.
While walking through Roundstone Woods she encountered the Fairies after spending her life looking for them. However, she saw them as good, friendly creatures, which Jack disagreed with her on. She never realised their true nature until in 2007, they killed her by invoking a heavy storm above her. Jack was greatly upset. (TV: Small Worlds)