This summer my daughter Adriana, 12, and I were wandering along the river near our home in Hampshire.

The sun was streaming down; I had a takeaway coffee, she had a juice and we chatted away.

As we came to sit on a patch of grass by the water, I decided I should reveal a secret I’d been keeping for 12 years.

So I took a deep breath and simply told her straight: ‘You were supposed to be one of twins, but one didn’t make it.’

Some mothers might think it a strange place, or age, to raise this emotive topic. But the time felt right. Adriana has always been very mature and emotionally intelligent – and it was now or never really. I feared if I didn’t tell her soon, I might one day blurt it out and she’d accuse me of having hidden it from her.

My story echoes that of Love Island star Olivia Bowenwho spoke movingly about losing one of the twins she was carrying to Vanishing Twin Syndrome in a ITV documentary this week. She was told she had been expecting twins but that one had stopped growing in the womb.

Vanishing Twin Syndrome is a type of miscarriage where an embryo detected during an ultrasound can’t be found in subsequent scans. The embryo stops developing, and gets absorbed by the mother or even the surviving baby.

Guesses vary as to how common this phenomenon is, with some experts saying it can happen in as many as one in eight natural pregnancies and up to a third of IVF pregnancies.

Mine was a natural pregnancy. When I became pregnant with Adriana in 2013, aged 36, my husband Cornel and I already had our son Alex, then four. Before our son, I had suffered two miscarriages. I had to take progesterone to prevent miscarriage again while pregnant with Alex, so I was already nervous.

But this time felt different.

With Alex I had severe morning sickness. With this pregnancy, nothing. Yes, I felt the usual aches and pains, the pulling of ligaments and tiredness – but other than that all was well.

At eight weeks, we went for an early scan due to my miscarriage history.

Cornel sat at my side as the sonographer showed us images on the screen. She showed us a tiny foetus, wriggling away and I sighed with relief.

Then she paused and focused on another area of the screen. She zoomed in, then said: ‘Oh, and another one!’

I gaped. I actually said: ‘Pardon?’ ‘Twins,’ she smiled. Then she looked a bit more serious. She did measurements and calculations which took a long time.

Then she said that while both had heartbeats, only one baby was the right size for its age – the other was a bit smaller.

‘We’ll do another scan in two weeks,’ she said.

I went home in shock. First that we were expecting twins – at the time we were living in a one-bedroom flat with our son and I did worry how we’d manage. But secondly, I was terrified about one twin being smaller. Still, I ‘felt’ very pregnant – exhausted, emotional, achy. As long as I had those symptoms I told myself I’d be OK.

Two weeks later, we went back for our scan. That morning I had a really strange feeling, as if I was ‘less’ pregnant. I ached less. I felt more with it. I told myself I was just being paranoid.

At the scan, the sonographer pointed out one healthy twin. Then she focused on the other. Two weeks previously it had been wriggling too. This time it was motionless. Still.

‘I am so sorry…’ she began.

There was no heartbeat.

Twin one was doing fine. Twin two had died. I didn’t cry, I just fell silent. The room seemed eerily calm as Cornel squeezed my hand.

We went home, clutching our scan printouts. Macabrely, perhaps, I had asked for a picture of both twins together, even though one was no longer alive.

I sat and stared at the image.

Thoughts raced around my head ranging from grief, to shock: Why had this happened? Did it mean I’d miscarry the other twin? This was my third miscarriage? Could the other twin survive?

I spent the rest of my pregnancy terrified, checking my bump, ensuring I could feel the baby moving. I’ll admit I fell into a kind of depression at times, thinking about what could have been – two twins playing together, growing up together, two cots, the works.

At 20 weeks, we went for another scan and found out I was carrying a girl. The sonographer knew I had lost a twin.

She scanned my stomach and showed me a tiny, tiny fleck on screen.

‘That’s the twin. The body slowly absorbs it,’ she says. ‘It’s called Vanishing Twin Syndrome.’ It was the first time anything had been said about this syndrome. But my Google searches told me it was surprisingly common. In the ‘old days’ before scans, women just never knew. Often the midwives would find the dead twin in tiny, flat ‘papyrus’ form, or absorbed into the placenta, or just not there at all.

I was relieved our surviving baby was well. We named her Adriana. As she grew I’d often wonder what her twin would have looked like. Was it a boy or a girl? Would they have been identical or looked different?

My grandmother had been an identical twin. It would have been like life coming full circle. Adriana grew and loved dolls, My Little Pony, face paint, make-up and Barbies. She played happily alone but sometimes I’d watch her and wonder if she felt that loss of the twin she could have had. Was she subconsciously aware of the loss?

Then, when she was around seven, she met twins at school and said something that gave me chills: ‘I wish I had a twin, Mummy.’

That night I wept. I’d kept it in for years, telling myself it was for the best, even making light of it with friends saying, ‘How on earth would I have coped with twins?!’

But now, as she said this, something in me that I’d been keeping locked away swam to the surface.

She had been a twin. They had shared the womb side by side for ten weeks. Was there something in her that knew this, even remembered this, at some psychic level?

The years passed. Then came that summer day this year when we walked by the river. I’d always wanted to tell Adriana – I just felt that she should know.

She’s a very emotionally aware girl, very bright and empathetic, so I felt sure she could handle it.

All the same, I did hope I wouldn’t upset or scar her. In the end, she looked shocked. Then she had a little cry, as I did too.

I hugged her then.

‘I wonder what he or she would have looked like,’ she said. ‘I wonder if it would have been a girl?’

A lot of mothers may feel that 12 is too young to share something that could feel rather momentous to a child, but I know my daughter.

In the times she has mentioned it since, she seems very at ease with the knowledge. So I am glad I told her.

It’s not the same as losing a baby later in pregnancy, or – God forbid – a live baby or child, so I do not try to compare my loss to anyone else’s.

It was an early loss, so early that many people might not have even known without the scanning technology we have today.

But I have kept those scan images of the two babies side by side. They’re stored away in the attic. I can’t bear to get rid of them somehow.

They’re the only pictures that showed that for ten brief weeks my daughter’s twin existed.