Sadie Brittle, 32, and husband Gary, 36, were devastated when they lost their baby just eight weeks into the pregnancy on 26 April 2016.
But earlier this month Mrs Brittle returned to her GP after feeling unwell and noticing her stomach was getting bigger while on holiday.
Initially she believed her symptoms were being caused by pregnancy hormones which were still present in her system from her miscarriage.
However, doctors discovered a tiny second embryo developing normally in her uterus and realised she had what's known as a "heterotopic pregnancy".
"The midwife told us that in the 23 years she's been working, she's never come across it and that she'd only heard of it before," the mum-to-be said.
The couple, from Staffordshire, are now looking forward to the arrival of a baby boy, in November 2016.
Brittle originally discovered she had suffered an ectopic pregnancy - when the foetus develops in the fallopian tube - after undergoing a routine hospital check-up.
"I was coming back in the car from having some tests done and I felt really hot and my vision went all blurry," she said.
"I went back to work at the hairdressers and said I can't cut anybody's hair because I didn't feel well.
"I scared myself when I looked in the mirror because I'd gone white and my face was sweating - I felt like I was actually passing out.
"My friend at work called Gary and he called an ambulance, my blood pressure dropping was a sign of internal bleeding.
"I had two scans and they suspected it was a ectopic pregnancy so I had surgery that night to remove one of my fallopian tubes, as well as two blood transfusions.
"They said that babies in this situation are normally in the middle of the tube, but mine was right up near the top where all the blood vessels are.
"I was in hospital for five days and was on antibiotics and pain relief - they said I would still be able to have children because of the other tube."
After recovering from her surgery, the couple, together with their four-year-old daughter Summer, went to Spain on holiday.
The mum added: "I was on a sun lounger and wondered why my stomach was still big and quite high up.
"I took a pregnancy test and it showed that I was pregnant, I thought there's no way that I am.
"We called the midwife from Spain and she said it could either be a multiple birth or a few cells were left in my body after surgery which would make it look like I was still pregnant.
"I went to see my doctor when I got back and explained my situation and he couldn't quite get his head around it. I had an ultrasound and you could hear a heartbeat.
"I went for a scan which showed that I was 19 weeks pregnant.
"Most people who have heterotopic pregnancies find out when they go for a ectopic scan, but mine wasn't picked up due to being eight weeks pregnant - and because I was really poorly, they must have just focused on that problem."
The couple went for their 20 week scan at Good Hope Hospital in Sutton Coldfield, that revealed their son was progressing normally.
"The scans show that he's healthy and I've been through it before so I'm just excited," Brittle added.
Her husband Gary, a building maintenance engineer, said: "To have this type of pregnancy is a one in 30,000 chance, so it's a miracle.
"It was such mixed emotions, we'd gone through dealing with the loss of the baby and then all of a sudden to be told that we've got another baby in there. It makes me want to buy a lottery ticket every day.
"Our daughter Summer must have known something we didn't because when we were on holiday we went in a shop and Summer pointed to some milk and said 'we need to get some milk for the baby'.
"We tried to explain again that mummy was having a baby and now she's not but Summer just started clenching her fists and gritting her teeth and said 'you don't understand, there is a baby,' so she's probably a bit psychic."