A UK woman with two wombs is believed to be the first in the world with the condition to give birth to triplets.
Hannah Kersey, 23, from Northam in Devon, had identical twins Ruby and Tilly, who were born from one womb, Grace, who was born from the other.
The girls had to stay in hospital for nine weeks after being born seven weeks early by Caesarean, but have now returned home to their parents.
The odds of having triplets from two wombs are about 25 million to one.
The chances of a woman with two wombs having twins or two separate births is estimated to be five million to one.
Only 70 women in the world are known to have been pregnant in two wombs, reports suggest.
The condition, which is actually called uterus didelphys, affects one in 1,000 women in the UK.
In Miss Kersey's case, the babies were conceived from two eggs - one in each womb - which were fertilised at the same time by two different sperm.
One egg then divided, producing identical twins, while the other developed into a single baby.
Mr Ellis Downes, consultant obstetrician and gynaecologist at Chase Farm Hospital in London, said: "It is quite amazing. Women with two wombs have conceived a baby in each womb before but never twins in one and a singleton in the other."
Leading expert Mr Peter Bowen-Simpkins added: "For a woman to spontaneously conceive and give birth in this way is a real rarity. They have been extremely fortunate."
Mr Richard Warren of the Royal College of Obstetricians and Gynaecologists said most cases occur naturally, but the condition can run in families.
Hannah's mother and sister also have two wombs.