Safa and Marwa were born joined at the skull, they've never been able to see each other's faces.

There are no official figures for how often this happens, but one estimate says craniopagus conjoined twins are born once in every 2.5 million births.

Most do not live longer than a day.

To separate them required multiple surgeries, months of hard work and the expertise of hundreds of hospital workers.

The BBC was given exclusive access to Great Ormond Street as surgeons worked to separate the two girls.

Video by Fergus Walsh, Rachael Buchanan and Laura Foster.

Our World: Two Brains, One Skull - Separating Conjoined Twins can be seen on BBC World News and the BBC News Channel at varying times over the weekend of 20 and 21 July 2019.