London - No parent ever forgets that first proud procession from the car to the family home. Ali Sanders remembers every tiny detail of the day she brought her twins home - the baby seats "took up the whole of the back seat", she says.
She watched as her husband, Michael - already "head over heels in love" - clumsily fussed over the straps and buckles, like the excited novice dad he was.
Then, inside the house, came the other big family milestone - meeting the "over-the-moon" new grandparents. "I remember Michael’s dad meeting them," says Ali, 35. "He said: 'Here’s Grandad!' He was so happy. Everyone was. My parents were thrilled, too."
Of course they were: this was the fairytale ending to Ali and Michael’s struggle to start a family.
Just after Christmas in 2014, their prayers were answered. They were approved to adopt adorable, eight-month-old identical twin boys who even looked like Michael.
"They were chunky and squidgy, with huge brown eyes," says Ali. "Absolutely gorgeous."
The couple spent the next six weeks gradually getting to know "their" babies, visiting them at the foster home where they had been placed, decorating their nursery and preparing for the big "take-home day".
Life could not have been more perfect - in theory. Only something was wrong with Ali. She wasn’t "getting it", she says.
She remembers taking the boys to the park for the first time in the beautiful new double buggy she had "obsessed" over for months.
Motherhood often feels overwhelming and adoptive parents are not spared the waves of panic. There is even a condition called "post-adoptive depression".
But this was something else. She realised she was pregnant after taking a test.
Shocked, Ali and Michael called their social workers. And that was that. By the end of the day, the adoption process was off.
"I told the social worker I didn’t think we would be able to keep the twins," says Ali, tearfully.
The babies went back to their foster parents that very evening.
Now, with the benefit of hindsight, Ali thinks that from the moment she was pregnant the adoption was doomed, because her body simply refused to allow her to bond with babies that were not genetically hers.
Now, she says, every time she sees twins of that age, she wonders: "Could that be them?"
Her greatest wish is that one day the boys will come knocking on her door. She has drafted a letter which the adoption agency says can be put on their file. What does it say?
"That it wasn’t their fault, that they did nothing wrong, and that I’m sorry we let them down."