Spoilers up to and including 'The Snowmen'.
River knew. She had known for a long time.
There was a moment they had shared, right after they had gotten married and on her first of many nights inside the TARDIS. An opening of minds so to speak. It was a very close gesture that only married couples usually participated in since it required the use of the others real name (which was always powerful) and quite a bit of intimacy with your partner.
She found out just after they had shared the bed (he knew how to please a lady) and minds for the first time (such a wonderful feeling). The Doctor had fallen asleep, but he was relaxed and his mind was still partly open. It was also the first night she witnessed his nightmares.
They didn't start at first. River stroked his hair until she fell asleep beside him. It was hours later when his dreams accidentally leaked into her mind through the still open link that she saw it葉heir first and last meeting in the library. Her death. She was startled awake, staring blankly into the depths of their shared room. She couldn't believe that just happened. Why did the Doctor stay with her if he knew her death? She never did find that out.
After River had collected herself, she ran her fingers through the Doctor's hair again to keep the rest of the nightmares away. She kept it up for the rest of the night, and it worked...for the most part. She had fallen asleep around dawn only ten minutes before the Doctor woke up from one of the best nights of sleep he had in a long time and snuck out of the room to go and attempt to make breakfast for the two of them.
It's been many years since then. River and the Doctor ran, so much and so far. She never wanted it to end, but then she got the opportunity to go to the Library. Despite what she knew, it wasn't something she could pass up.
The Doctor took her to see the Singing Towers. They were beautiful and he cried. Looking into his eyes, she knew why he did, but he didn't know she knew, so she had to ask him, but he didn't answer.
He dropped her back off at home with a kiss and a modified screwdriver, and she planned. She would not die at the Library. It would not happen, she wouldn't let it. He had his heart broken enough for one lifetime.
The Teselecta was not an option. That current would fry their systems, killing everyone inside. She needed a way to die without dying.
Her eyes widened in realization. A way to be you, but not be you揚angers! Mother was a ganger while she was pregnant. The Doctor once told River they made a ganger of her when she was a baby to trick mother into thinking she was safe.
River found a place where you could have a ganger made, and for one week, she lived with the ganger in her house, making sure it not only understood its job, but could act like her. It was like living with a twin.
When the week was up, the ganger went to meet with the expedition and River sent the Doctor a message on the physic paper. Ganger River knew of the message, but wouldn't have an opportunity to send it while surrounded by her colleagues.
Two days later, the memories of the ganger were transferred into her head via a physic link they set up. She cried. River knew that the look on his face would hurt her, but until she saw it, she didn't know how much. He was so young.
River had to leave. She was thought dead in this century anyway. Besides, it was illegal to send gangers to do jobs, regardless of the skill level, unless the gangers were authorized. If anyone found out she sent a ganger to the Library, she would be facing charges.
She packed up everything important and vanished from the fifty-second century, reappearing in twenty-first century London, the Doctor's favorite time and place.
It didn't take her long to find a flat and a teaching job that paid well. All she had to do was wait for the tell-tale sound of the TARDIS.
It was another year before she not only heard the sound of the TARDIS in downtown London, but found the correct version of the Doctor. He wasn't alone; River didn't know his new companion.
The brown haired girl looked around in wonder at first and then disappointment at her surroundings. She must be from modern day London, like most of his companions, but River could tell she was good for her husband. He ignored her disappointed look at the familiar landscape and smiled anyway, talking one hundred miles a minute to the girl. He was so sad after Manhattan, and then River going to the Library must have killed him. She was glad he found someone to show the universe to.
The Doctor led the young girl away towards a fish and chips shop where they got their orders and sat down in a booth, the Doctor facing away from the door.
River pushed herself off the wall and crossed the busy street. She stroked the outer wall of the TARDIS when she passed and could hear its hum in the back of her mind. She had missed her child. River smiled and patted the box one more time before walking to the shop and stepping inside.
The Doctor's new companion looked up, saw her, then looked back down at her chips, uninterested in the random customer. Oh, how that would change in a matter of minutes. River ordered her own order of chips because she knew if she stole off the Doctor, he wouldn't be happy. This regeneration really enjoyed his chips, although River thought it was a leftover from his previous regeneration and Rose Tyler's influence.
She thanked the man at the front and paid, taking her basket of chips over to the duo in the booth. The companion looked up as she heard her walking over, but the Doctor was oblivious as ever, rambling away about this, that, and the other thing.
River rolled her eyes and pushed her way into her husband's side of the booth, nudging the Time Lord over with the slightest of pushes to make room. It was just too easy to squish him over.
"Hey!" he shouted, spinning to face her and froze.
River smirked. "Hello, sweetie," she said and gave him a chaste kiss on the lips before taking one of his chips and eating it.
"Yes, sweetie, it's me. Don't look so shocked."
River sighed and looked at the new companion. "As it seems my husband is in shock, I'm Professor River Song." She held out her hand.
"Clara." They shook hands. "Husband?"
River ate another chip. "Yep."
Clara looked confused. "But he said you were dead."
River nodded. The Doctor was still in a bit of shock. She smiled at him. "Bless." Then turned back to Clara. "It seems that it's illegal to have a ganger go to a professional job in your place." River shrugged. "Oh well, I was getting tired of that flat anyway."
"River, wait," the Doctor said, interrupting her. "Where are you?" He pulled out his diary and started flipping through it, trying to figure out where they were based on what she's already said.
"Where are you?" Clara asked.
River looked away from the Doctor and back to Clara. "We kept meeting in the wrong order. My lasts were his firsts, and vice versa." River smiled sadly, putting her hand over his diary to push it out of his line of vision. "And sweetie, I died. At the Library. We're in sync." The Doctor looked at her in shock. River smirked. "Unless of course you've been doing something naughty with a future version of myself." She winked. The Doctor swallowed thickly.
"Um...no, no, I um..." He glanced at Clara and back to River. "Umm."
River laughed. She loved seeing him all flustered. "Well, now that that's all sorted out and the chips are cold. We just need to make a quick stop off at my flat to get my things and tell the land lady I'll be leaving and then we can be on our way.
The Doctor shook himself out of his shock and ran to catch up to River, cold chips forgotten on the table, who was already unlocking the door to his beloved Time Ship. Clara followed behind.
"River, what are you talking about?"
River rolled her eyes from the other side of the console in front of the screen entering coordinates. "You daft old man. I can't believe I have to spell it out for you," she said to herself. She walked around and stood in front of him. "I'm going to travel with you. There's nothing left for me in the fifty-second century. I've already visited mum and dad for the book and they're happily living their lives. Brian knows what happened and doesn't expect to see me that often. My job was temporary anyway. Never really did like teaching. I'll call the school and let them know I'm quitting when we go to my flat and get my clothes. All loose ends are tied up, sweetie. Now stop worrying about me and figure out where you want to take us after I get the last few things sorted." River turned back around and started flipping switches to land the TARDIS in her flat.
After taking care of everything, the Doctor steered the ship into deep space and let it float around for a while. Clara had gone to bed after the long day and River and the Doctor were sitting in the doors staring out at the stars.
River was leaning on the Doctor, her head resting on his shoulders. "She's good for you."
"Clara. She's nice and she's good for you. You needed someone who can look after you, but still look amazed when you bring them to a new planet."
The Doctor stroked his thumb over her hand. "How long did you know?"
"About the Library?"
"Since the first night."
"Why didn't you say anything?"
"Same reason why you didn't, sweetie." The Doctor stayed silent.
River sat up and stared at him. "For what?"
He shrugged. "For everything."
River kissed him. "Don't you dare apologize for anything that happened. I don't wish to think what life would have been like if I had never met you, Theta. That thought alone terrifies me and I hate it." The Doctor stayed silent. "I know you're blaming yourself. I know you, sweetie, but not everything is your fault. For all the bad things that happen around you, there are hundreds of more good things and without the bad, you can't have the good." River stood up and stretched. "Now come on, there's something I want to show you in the bedroom."
The Doctor smirked and stood up, closing the outer doors. "Well, then Professor Song, lead the way."
"Oh I will, sweetie," she purred, pressing him into the closed doors and shrieked when he slapped her bum.
She pouted. "That wasn't very nice, Theta."
He placed his hands on her hips. "I wasn't trying to be nice, River."
"Oh a bad boy tonight then?" She turned around and grabbed his hand. "Well, come on, then, bad boy, let's go to the bedroom and you can show just how bad you can be."
As the couple left the main console room, the TARDIS dimmed the lights and hummed happily. Her child and her thief were back together and all was well.