Amy was, for once, bored. So she decided to do the logical thing: explore the TARDIS. The Doctor was messing around under the console, so she wouldn't be missed for a little while. She wandered the corridors, peeking through doors as she went. Amy found a kitchen, several guest bedrooms, the missing swimming pool, and finally, a library. Intrigued, she stepped inside, eager to find out what kind of books the Doctor read.
To her surprise, she found mainly biographies, with the odd mystery or thriller thrown in here or there. There was a small table set to the side along with a few chairs. A book lay open on the table. Upon closer investigation, she saw the page had been markedwith a beautiful charcoal drawing.
The picture showed a young girl, with short, curly black hair and a loving smile. Though the picture was in black and white, you could see the sparkle in her eyes. The artist had lovingly written 'Susan' at the bottom of the picture. Some intuition told her the Doctor himself had drawn the picture. Amy had an inkling of jealousy. Who was this girl? And why was she so special to the Doctor?
"Amy?" The Doctor appeared in the doorway. He saw her standing next the the picture and sighed. "I knew I should have put that away."
"Who is she?" Amy asked sharply. The Doctor sighed and ran his hand through his hair. His normally cheerful demeanor now had an melancholy expression.
"My granddaughter," The Doctor answered. He saw her expression. "Yes, I know, I'm older than I look, you know. Why shouldn't I have a family, anyway? I had a wife, children... and I had Susan." He came over and looked at the picture."What happened to her?" Amy couldn't stop herself from asking.

"She traveled with me for a while. Then she fell in love. I left her in 22nd century earth, visited a few times but... it's painful. Bittersweet. Sometimes its better just to have the memories."

"How old are you really, then?" Amy asked curiously. The Doctor smiled.
"Why?" he asked. "So you can throw me a birthday party?"