Brazilian twins who were joined at the head have been successfully separated with the help of virtual reality.
Three-year-olds Bernardo and Arthur Lima underwent surgeries in Rio de Janeiro, with direction from Great Ormond Street Hospital in London.
The teams spent months trialling techniques using virtual reality projections of the twins, based on CT and MRI scans.
It was described by surgeon Noor ul Owase Jeelani as "space-age stuff".
It was one of the most complex separation processes ever completed, according to the charity which funded it - Gemini Untwined - which Mr Jeelani founded in 2018.
He said that, for the first time, surgeons in separate countries wore headsets and operated in the same "virtual reality room" together.
The twins had seven surgeries, involving more than 27 hours of operating time in the final operation alone, and almost 100 medical staff.
Speaking about the VR aspect of the surgery, Mr Jeelani told the PA news agency: "It's just wonderful. It's really great to see the anatomy and do the surgery before you actually put the children at any risk.
"You can imagine how reassuring that is for the surgeons.
"In some ways these operations are considered the hardest of our time, and to do it in virtual reality was just really man-on-Mars stuff."
He said that previously unsuccessful attempts to separate the boys meant their anatomy was complicated by scar tissue, and he was "really apprehensive" about the risky procedure.
Mr Jeelani said he was "absolutely shattered" after the 27-hour operation, where he took only four 15-minute breaks for food and water, but it was "wonderful" to see the family feeling "over the moon" afterwards.
He added that, as with all conjoined twins after separation, the boys' blood pressures and heart rates were "through the roof" - until they were reunited four days later and touched hands.
The twins are recovering well in hospital, and will be supported with six months of rehabilitation.
This was Mr Jeelani's sixth separation procedure with Gemini Untwined, after previously operating on twins from Pakistan, Sudan, Israel and Turkey.
He led the procedure alongside Dr Gabriel Mufarrej, head of paediatric surgery at Instituto Estadual do Cerebro Paulo Niemeyer in Brazil.
Dr Mufarrej said the hospital where he works has been caring for the boys for two-and-a-half years, and their separation will be "life-changing".
"Since the parents of the boys came from their home in the Roraima region to Rio to seek our help two-and-a-half years ago, they have become part of our family here in the hospital. We are delighted that the surgery went so well."
Bernardo and Arthur, at almost four years of age, are the oldest craniopagus twins - that is twins with a fused brain - to have been separated.
According to the charity, one in 60,000 births results in conjoined twins, and only 5% of those are craniopagus.