Out of all things, Twilight got pregnant in the human world after a party with the girls and a few two many beers, which ended up with Twilight waking up in Flash’s bed.
 
Of course, Twilight didn’t realize this until she came back to Equestria, and quickly learned that her cycle had been changed due to her constant watch of it. She worried about the foal inside her, how interspecies and inter-universe breeding might work out at all. Twilight knew she had to tell Flash, so she went back to the human world through the mirror to meet with him.
 
Needless to say, Flash was very displeased and frankly frightened of the idea of having a baby, especially one with a pony princess from another world. After a long conversation about child care, interspecies crossing, and more, Flash decided he didn’t think he could handle a baby at all. He didn’t think he was mature enough to help her raise it, between worlds no less. Twilight tearfully left, but understood why he might not wish to raise such a child.
 
It was twenty months later before she gave birth to her foal. She had no idea why it could have taken so long, but after a bit of research she found that humans usually give birth after nine months, while ponies took eleven. The child was strange, with Flash’s human half where the head should have been, and a pony half where the hips and legs of a human should have been. It was very small for a foal, and quickly had to be taken into medical care.
 
It was months later when Twilight was finally able to take the filly-girl home. She named her Half-Light, due to her being both half pony and half human. When she was finally older, Twilight decided to take Half-Light to meet her father in the human world. Surprisingly enough, she remained the same even though Twilight transformed into a human once more.
 
Flash was very surprised to meet his daughter, and seemed mesmerized that she was half-pony. He asked if this meant his daughter was a princess. Twilight said she was.
 
After a long conversation, Flash and Twilight agreed to have joint custody of Half-Light, where every two months Half-Light would go to the human world to spend time with her dad, and return after two months. This way she could learn from both worlds, both human and pony. Although, ponies were infinitely more understanding towards Half-Light’s hybridization (if a little hesitant due to the Tirek incident and their same body structure), while she couldn’t be around humans other than the Humane Six and Flash.
 
Half-Light is very intelligent if rebellious filly-girl, and wishes very much so to reveal herself to the human world and hopes to be accepted. Although she does understand why she shouldn’t, due to horror stories of what people do to creatures that are not like them. Half-Light is very self-conscious but makes up for it with her ego that she puts on, due to Rainbow Dash. But she’s also very kind, if stubborn.