When Adel and Blane Pearson discovered they were having twins three years ago, they thought it was a fantastic surprise. But the couple were stunned when Adel fell pregnant a second time - and learned she was again expecting twins.
Now they are regarded as a 'one in a million' family by experts because the first set of twins - Grace and Ruby - are non-identical while the latest arrivals - Isla Mae and Isobel - are identical.
All four girls were conceived naturally, without the need for any IVF treatment, and there is no history of twins in their families.
But it means Adel, 30, and Blane, 35, go through 100 nappies a week and have to plan everything like a military operation, such as the children's feeding, bathing and getting them dressed.
Debbie Ross, membership manager of the Twins and Multiple Birth Association, described the Pearson family's two sets of twins as 'practically unheard of.'
'The chance of having non-identical twins is one in 67 while the chance of having identical twins is about one in 1,000', she said.
'But the chances of having two sets of twins, identical and non-identical, must be one in a million. You will find very few families who have a pair of identical twins and a pair of non-identical twins.'
Non-identical twins Grace (7lb 6oz) and Ruby (7lb 8oz) were born on December 9, 2005 - although the twist was that the girls look identical.
Identical twins Isla Mae (7lb 6oz) and Isobel (8lb 6oz) were born on August 26 this year.
On both occasions Adel was induced at 38 weeks pregnancy, managing to carry her babies nearly all the way to full-term. Both sets of twins were also born through caesarean section three minutes apart.
But the joy of the arrival of their first set of twins turned to near-tragedy when Adel collapsed shortly afterwards with a blocked artery in her lung and a hernia and almost died.
She was in hospital for five months fighting for her life which meant Blane had to look after Grace and Ruby alone at home.
'I was so ill and it hurt so much not being able to see my baby girls being raised. Blane was an absolute hero, doing the job of two of us while I was ill, Adel said.
'When I finally came out of hospital it was a enormous shock. I had to get better quickly and become a mother but with twins it was double the effort.
'To start with it was a nightmare telling them apart, so much so that I had to put tags on the end of their feet to make sure which one was Ruby and which one was Grace.'
The couple decided they wanted another child quickly to 'complete their family' so decided to try again to conceive.
Adel, 30, said: 'We weren't looking to have another set of twins but after I knew I was pregnant again I could see immediately that my belly was already very big.
'When I went to see my GP shortly before the scan he said to me, "I can say the chances of you having another set of twins is so rare it's not worth thinking about - it would be unprecedented."
'But then it happened. We went for our first scan at 13 weeks of the pregnancy and they told us I was expecting twins again.
'We didn't know how to react, we both just burst into laughter.
'I wouldn't know what to do with one baby on its own. My first thoughts were that this is going to be absolute hell but now I just find myself having to be very organised everyday.'
Although the first set of twins are technically called identical, Adel was certain that the second pair who are non-identical twins look more alike. She also believes they each have their unique own personalities.
'They're so alike in appearance but but actually the girls are poles apart in some ways', she said.
'Ruby and Isobel are nothing like their sisters character-wise. They both like their own way and can be very demanding. Grace and Isla Mae are more thoughtful. They like to take time to think things out and are more laid back like their Dad.'
Adel admitted that the family had become 'minor celebrities' where they live in Colchester, Essex.
She said: 'I can barely go out now, me and the girls are like celebrities. I can't go shopping without somebody stopping me and wanting a look at the girls.
'I try to dress them differently but everyone sees through it. People are just fascinated and have so many questions to ask.
'I really hope that they don't pair off and gang up against each other but at the moment it's just great to watch two pairs of very young twins forging a relationship together.'
'They are just fantastic.'