Alexandra and Calder Berney-Edwards are among the very few fraternal twins — that we know of, at least — with two different fathers
Adorable 19-month-old twins Alexandra and Calder are the spitting image of Daddy — or make that both their daddies.
Alexandra shares father Simon's big brown eyes, while Calder's piercing blue gaze makes him a doppelganger for his father, Graeme.
'Dada, Dada, Dada,' they chorus as they swap places on the laps of their devoted parents.
It's their favourite word. And what about Mummy? Well, that's a bit more complicated.
They have a 'tummy mummy', a Canadian surrogate called Meg Stone — a 32-year-old single mother of two sons aged 12 and six — who carried the IVF twins for the British same-sex married couple.
Then there's the twins' biological mother, an anonymous American egg donor about whom the family knows almost nothing, apart from a detailed medical history.
For sure, this will make for a very interesting bedtime story when the twins are old enough to understand.
For Alexandra and Calder Berney-Edwards are among the very few fraternal twins — that we know of, at least — with two different fathers.
Usually born to super-fertile mothers who have been intimate with more than one man while ovulating, these cases normally come to light only when paternity is questioned.
But Simon and Graeme's one-of-each twins were very much planned — and at considerable cost — although they insist vanity played no part, nor a desire to pioneer a fashionable trend in the brave new world of assisted fertility.
For while there is greater acceptance of families with same-sex parents these days, Simon and Graeme are painfully aware there are still some people who do not approve. Even a few gay acquaintances were, they say, 'dismissive'.
'Sometimes people stare, and we can see them having little private conversations about us, but on the whole most people are very accepting,' says Simon.
'We've always said we will be very upfront with the twins as they grow up, explaining their heritage in an appropriate way. There is so much diversity these days that having two dads is not quite as shocking any more.'
Certainly, the parental landscape has changed dramatically within a short space of time.
When the couple first approached a clinic in Las Vegas three years ago, they imagined having only one child to begin with, possibly followed by a second a few years later — not unlike Sir Elton John and husband David Furnish's two young sons.
But when the question arose of who would father their first child — cue much discussion and indecision — the clinic suggested a twin pregnancy: implanting two embryos fertilised separately by each of their sperm, a practice not permitted in the UK.
The couple jumped at what sounded a logical and fair solution to their situation, and now, the two little ones are creating merry havoc in the kitchen-diner of their South-East London home, with toys and books spilling across the floor.
'We always said we didn't want to know whose child was whose because it really didn't matter to us,' says Simon, 43.
'But almost as soon as they were born it was pretty evident just by looking at them!'
With IVF fees standing at £25,000 — and that's without international flights, accommodation, surrogate expenses and lawyers' fees — the couple also realised two separate pregnancies would be financially crippling. So they went for the double whammy.
Even then, they had to remortgage their home, but they achieved their dream: the twins were born naturally in Canada on June 25, 2017, with both fathers — bursting with excitement — in attendance.
Alexandra was born first, at 6 lb 10 oz, and the couple had no idea which of them was the biological father.
But when Calder followed seven minutes later, weighing 7 lb 3 oz, there was no question of 'Who's the daddy?' He was the spit of Graeme as a baby.
'Holding them for the first time was just unbelievable, and I still feel emotional thinking about it,' says misty-eyed business development manager Simon, as he cuddles daughter Alexandra, who showers him with kisses.
'Picking up these two little beings and looking into their eyes was just so overwhelming.'
Former landscape gardener Graeme, 48, who writes a blog about being a gay stay-at-home dad, adds: 'There was just this huge wave of love. It was absolutely amazing. Every day, I feel blessed to have these two.'
But do they ever find themselves favouring their own biological child over the other? Simon shakes his head, insisting: 'I love them both equally and in different ways.
'Actually, at times I almost have a better relationship with Calder and Graeme has a better relationship with Alexandra, because it mirrors our relationship.
'Alexandra can sometimes really push my buttons because we're so alike, and Calder can push Graeme's.'
Certainly, the twins don't appear to have a favourite daddy. They are equally cuddly with both, swapping places in their arms without so much as a squabble.
And, despite their obvious genetic heritage, they have their own unique personalities.
Mischievous Calder goes by the nickname Cheeky Bear on account of the glint in his blue eyes and his determination to 'get into everything'.
He is also 'court jester' to Alexandra, or rather Little Princess Bear, whose steely, regal glare 'would stop a herd of stampeding elephants in its tracks'.
'She will make people work hard for that smile, but it's worth it,' says Graeme. 'Her daddies can usually be found wrapped around her little finger.'
Simon and Graeme, who met online eight years ago, agree the twins' arrival has turned their life on its head, not that they have a single regret.
Their smart terrace home, once a neat, orderly space, is now overrun with books, educational toys, clothes and two lively toddlers.
The days when Simon and Graeme could afford two or three holidays a year, plus 30 or 40 trips to the theatre, are a distant memory, and a large whiteboard on the wall lists meals, naps and kiddy activities.
'I love our new life, but there are moments when it's pure pandemonium and you think: 'Please just stop!' But there's something very lovely about having two children chattering away in the back of the car,' says Simon.