Wow the linked article is quite something:
https://en.wikipedia.org/wiki/June_and_Jennifer_Gibbons
> According to Wallace, the girls had a longstanding agreement that if one died, the other must begin to speak and live a normal life. During their stay in the hospital, they began to believe that it was necessary for one of them to die, and after much discussion, Jennifer agreed to be the sacrifice.[4] In March 1993, the twins were transferred from Broadmoor to the more open Caswell Clinic in Bridgend, Wales; on arrival Jennifer could not be roused.[5] She was taken to the hospital where she died soon after of acute myocarditis, a sudden inflammation of the heart.[5] There was no evidence of drugs or poison in her system, and her death remains a mystery.[6] At the inquest, June revealed that Jennifer had been acting strangely for about a day before their release, her speech was slurring, and she said that she was dying. On the trip to Caswell, she had slept in June's lap with her eyes open.[3][7] On a visit a few days later, Wallace recounted that June "was in a strange mood". She said, "I'm free at last, liberated, and at last Jennifer has given up her life for me".[5]