One of the disadvantages to The Doctor's new human body was that it required a lot more sleep than he ever needed as a full Time Lord. Although annoying, he found that the inconvenience of additional sleep was well worth it if it meant having Rose wrapped in his arms for those extra hours. Having only been back in what he had cleverly dubbed 'Pete's World' for a few weeks they were both still tentative as they relearned one another after their long separation, neither of them quite ready to move to a more physical aspect of their relationship just yet but still unable to bear being apart for long periods of time, so they had agreed to share a bed while still taking things slow.

It was a quarter after one when he came awake, reaching out and finding the left side of the bed once again empty and slightly cold. Stretching, he got up and walked over to the chair in the corner of the room, picking up his t-shirt and slipping it on as he made his way down the hall to the spare room. The first night it happened he had been frantic. Waking up to find her gone after everything that had transpired on that godforsaken beach just a few hours prior sent him into a state of panic that almost rivaled the one he suffered that day at Canary Wharf when he was forced to watch as Rose's fingers slipped from that damn lever. He had practically leapt out of bed; tearing through the flat until he had finally located her in the spare room, curled up next to the makeshift tank he had built that housed their growing baby TARDIS and humming quietly. The relief he felt was almost palpable as he stared down at her, part of him wanting to inwardly berate her for scaring him while another part couldn't help but feel touched at the sight before him. He had called her name quietly, not wanting to startle her, but after several attempts of trying to get her attention he realized she wasn't even properly conscious.

He had asked her about it the next morning but she couldn't seem to remember anything besides a dream in which she heard the baby TARDIS singing and how much she had missed that sound after their separation. The Doctor knew Rose had a connection to the TARDIS that he could never quite fathom after she absorbed the entire vortex and became the Bad Wolf, so it seemed only natural that she would be able to connect with the small piece of coral on that level. At the time, he had decided to let the matter drop but then it happened again the next night, and the next, and every night after that since. In all the time they had traveled together, he had never once known Rose to sleepwalk and it was starting to become disconcerting even though she would always be right back beside him in bed when he woke up in the morning, curled around him with her head resting on his chest.

As he quietly entered the spare bedroom, he paused, taking a moment to actually listen to the tune she was humming for the first time and his breath caught in his throat. The song was unmistakable. It was the same song that always played in the back of his mind until the moment his beloved ship had parted from this universe. One that he could only hears faint snippets of from the still growing TARDIS coral that would grow stronger with time and he felt the prickling of tears at the back of his eyes.

"Doctor?"

Pulled from his thoughts he looked down to see Rose blinking up at him confusedly before looking around the room. "Was I sleep walkin' again?"

"Yeah, and I think I've finally figured out why." he said with a soft smile as he knelt down in front of her. "I think she's been calling out to you." He glanced over at the tank. "Ever since you looked into her heart you've had a connection. One that I've never been able to fully understand. One that no one besides me has ever had." Reaching down for Rose's hand, he entwined their fingers. "She's just as much a part of you now as she's always been a part of me and when we lost you…" He choked on the words and looked away.

Squeezing his hand so that his eyes met hers once more, she gave him a watery smile and used her free hand to cup his cheek. "I know. I missed you both too."

Leaning in, he pressed a soft kiss to her lips and then moved to sit beside her, keeping their hands entwined and she laid her head on his shoulder as they both looked lovingly upon their 'baby'.

"Do you remember that song you were humming?" The Doctor asked after a beat.

Rose shook her head. "I hear it in my dreams sometimes but when M' awake and try to hum it out loud it jus' doesn't sound the same." She tilted her head up to look in his eyes. "You said you know it though yeah?" she asked and he nodded. "Would you hum it for me?"

Smiling warmly, he kissed the tip of her nose and shifted so that he could pull her into his arms, her head resting against his chest as he settled back against the bed frame and began to hum the familiar melody. After a few moments her eyes began to drift shut, the sound of his voice and the gentle rhythm of his single heartbeat against her ear soothing her to sleep. Not long after, she was vaguely aware of the sensation of being lifted into his arms as he carried her back to their bedroom, tucking her in beside him under the thick duvet and wrapping his arms tightly around her.

"Sweet dreams, Rose Tyler." The Doctor murmured, pressing a kiss to her hair.

A ghost of a smile flickered across her face as she snuggled into him further and he resumed humming the hauntingly beautiful melody. The sweetest lullaby, the song of the universe.

A/N: Reviews are welcome!