But Dade was born female, and when the pair first got together in 2008 theirs was a lesbian relationship.
After realising he was transgender, Dade began his transition to becoming a man aged 29 in 2011 - just before Tiffany became pregnant using a sperm donor.
Life coach Tiffany, 41, says: "When Dade told me he wanted to be a man, we nearly split. I'd left my previous husband because I believed I was gay - but I loved Dade and stood by him. Now we have our daughter, we're happier than ever."
Electrical engineer Dade, 33 - who has had full gender reassignment surgery - adds: "I couldn't keep living a lie. I'm so grateful Tiffany supported me."
He says: "Mum called me her 'beautiful little butterfly,' which I hated. I dressed like a boy from the age of three and when I was older I wore a coat all year to hide my figure."
Dade, who dated both men and women, says: "I didn't understand my feelings. I thought maybe I was bisexual, but I was scared of being different so I dated men. I even got married aged 18, but we split seven years later after drifting apart."
Tiffany says: "I'd been married before, too, but realised I was also attracted to women and we split. I came out to my family and when I met Dade as a woman I was instantly attracted to her - she was petite and sexy."
Six months later, the pair moved in together. But in 2010, Dade realised he was transgender. He says: "We were watching a TV documentary about being transgender and it finally dawned on me that's what I was. Initially I kept it to myself because I was terrified of losing Tiffany."
A year later, Dade confessed. He says: "I told Tiffany I wanted to be a man. She was shocked, but I explained I couldn't live a lie."
In November 2011, Dade began hormone treatment. Tiffany says: "He developed body hair, his voice gradually deepened and he became more muscular. I worried I'd no longer be physically attracted to him as a man, but that wasn't the case.
"We'd already talked about having a baby using a sperm donor and decided to go ahead - so while Dade was transitioning I was pregnant with our daughter!"
The couple documented Dade's transition on YouTube and are now looking forward to the future.
She says: "We've gone through so much, but most people have been supportive. People don't even realise Dade's past and are shocked when they find out!
"I'm so proud of him - we're just like any other family."