When little Dante is old enough, his parents will sit him down and ­explain that ­"Mummy couldn't have babies... so daddy did it for her." That's because this cute toddler was born into one of the world's most amazing families. His mum Emily was born a boy. And his father Cai was born a girl. Doctors were baffled, believing it was medically impossible for "dad" Cai, 24, to give birth, especially as Emily was also thought to be sterile. Cuddling their hazel-eyed son, now 22 months old, the proud ­parents explain how it happened. "We didn't plan on having a baby," says Emily, 28. "We didn't try to make it happen nor did we think it could happen. We were planning on adopting because, as far as we knew, having a baby on our own was ­impossible separately, let alone together. "How it happened is a mystery, but we're very grateful for it. I guess when two people love each other a lot, then a lot of special things can happen." It was love at first sight when the couple – whose surname we are not ­revealing for their protection – first met. Neither had undergone surgery but they were living as the opposite sex and moved in ­together within three weeks, knowing they truly understood each other. "Being transgender is a pain, actually, and ­certainly not something you do on a whim," says Emily. "Then I met Cai and it was ­amazing. I thought such things only happened in fairy tales." Office worker Emily was waiting for surgery to remove her male parts and had been taking female hormones since the age of 16. The couple had ­unprotected sex, but believed there was no risk of pregnancy because the ­formerly female Cai was on a high dose of the male hormone testosterone and was thought to be "chemically sterile". "I had long since resigned myself to the idea that I'd never be able to have biological children of my own," says Emily. Having been on hormones for close to a decade it was considered impossible for me." What's even more remarkable is that cautious Cai also had birth control injections just to be safe. But nine months on from their first date he discovered that   his ­"stomach upset" was in fact a baby. "I was seven months' pregnant and I didn't know it," he says. "I'd put on 18lbs but didn't feel the baby move." Emily, born as a boy called Scott, is Dante's ­biological ­father. She had a full sex-swap operation a few months after the birth, and admits she felt so broody during the preg­nancy she wished she could have given birth instead. Despite the unplanned, unorthodox pregnancy, the couple are now doting parents, each taking on the role of their new sex. Emily "breast-feeds" Dante with formula milk using a special attachment. "I've always felt like the mum," says Emily. "Regardless of anything else there is a lot of love in our family. We both ­absolutely adore our son, and the amount of joy he's brought us is amazing. He is being raised in a loving, nurturing ­environment. That's a fantastic way for a child to grow up. Our son is great. He's ­perfectly healthy in every way." Although Emily went ahead with her sex-swap operation to make her fully a woman, Cai says he is happy as he is. "As far as how we see each other, we're a heterosexual couple," says Emily. "He's a man but has female parts. I'm a woman that once had male parts." Emily, who looks so feminine that most work colleagues don't know her background, adds. "When I'm at work people just assume that I'm just an average mother with a kid and husband." The couple, who live in rural ­Penn- sylv­ania in the US, now star in a ­TV ­document­ary called Pregnant and Transgender. And as Dante grows up there will be no secrets. "We'll be upfront with him," says Emily. "We'll explain the situation, and that it doesn't mean anything is wrong or that he's different. We will say mummy couldn't have babies so daddy did it for her." Cai adds: "Some say we shouldn't have had a child, that we will confuse him growing up. But we'll say, ‘We did things a little differently but here you are." Cai admits going through a stage of questioning his decision to change sex. "I remember one morning watching a couple in church with a baby," he says. "It was physically painful for me because I am sitting there thinking that's what I want and I will never have." Now that dream has come true Cai says he knows exactly what his role is. "I really do feel like the dad," he says.