It turns him into Kate Upton, bustiest Time Lady to explore time and space!

As the console explained, regeneration incorporates a mix of random genetic traits from the individual and some random mutations, with external influences from one's environment, as when Nine regenerated into Ten and took on Rose Tyler's accent and subconsciously became someone more age-appropriate in looks for her.

Steve couldn't think of any of this as the regenerative process ran through his body, taking only seconds but feeling like minutes, hours. His torso shifted and crunched, his chest ached, at one point he was sure he felt something crushing his testicles, but all of it began to dissolve into a hazy orange light as not just a new body, but a new personality formed. The fabric of his clothing dissolved from the **** of the regenerative surge, not just forming a new face and personality but turning this unassuming dork into a Time Lord!

The TARDIS spun in wild, lazy arcs through the Time Vortex as its inhabitant suddenly snapped forwards, standing stock still for a moment. He could feel the TARDIS still moving, but it... it was over. He looked down at his hands, seeing his hands were dainty, with slender fingers. Then his eyes went to his nude form beneath it.

He was fairly slender, but... well, was he a he anymore? He staggered over to the console, walking oddly, as his centre of balance was lower and he, uh, didn't have anything between his legs anymore! Tits were flopping on his chest! Fucking tits! Peering into the console, he couldn't see anything for the text already there, so on instinct he pressed a couple of buttons to clear it and let out a gasp, a very feminine sounding gasp.

Blue eyes stared out of a round feminine face, blonde hair cascading down past the shoulders of her still 5'10'' body. Two huge tits, which she immediately knew to be 30H, hung from her chest, capped with cute pink nipples. Her new pussy was shaven clear, and Kate Upton's entire body covered in a gorgeous bronzer to make her curvaceous physique truly pop.

"Kate Upton?!" Steve screamed in an incongruously English accent, posh and clipped, with an English rose charm. "And I'm English?!" Steve's Scottish pride was wounded. "Why did you turn me into this... this... boobsy body!" No answers were forthcoming. "Fuck!" she cursed, her tits wobbling with every motion as she paced around.

"OK... OK... so, I can get used to this. This is me now. This is me now. What does this body like..." Steve mulled it over, not noticing his hips swaying with each step. "There's worse things than an immortal time traveller with big bodacious titties." Even with the oh-so-posh English accent, he instinctively referred to his chest in such a way. "Clothes! That makes sense!" Steve went to the console, tapping some buttons to bring back up the instructions. They were still at the chronometer, showing they'd arrived at wherever it had deemed a 'safe place'. "Safe? Nah, let's have some fun." Steve hit some buttons. "Let's go for a..." Her finger hovered over a knob, and she flicked it. "Fun place!"

And so, the as-yet-unnamed Time Lady spins off into time and space, not yet used to her new body and personality! What changes have yet to reveal themselves?