One of the twins was registered as the father on the child's birth certificate (referred to in court only as "P") – but it was determined that "it is equally likely that each of the brothers is P's father." The other twin, together with the mother, attempted to assume parental responsibility by asking judges of the Court of Appeal to overturn an earlier decision by a family court judge. However, Sir Andrew McFarlane, sitting with Lady Justice King and Lord Justice Stuart-Smith, said that although they cannot determine who the father is, the person registered on the birth certificate will no longer have parental responsibility until the court hears further arguments. He noted that DNA testing shows either twin could be the father but cannot distinguish between them, so there is a 50% chance the true father is already registered on the birth certificate, according to the Mirror. The judge expressed hope that further advances in paternity testing would allow the family to get an answer by the time the child reaches adulthood. In a ruling delivered earlier this month, he said: "The current truth about P's paternity is that the father is one of these two identical twins, but it is not possible to say which. It is possible, indeed likely, that by the time P reaches maturity, science will be able to identify one father and exclude the other twin, but in the near term this is not possible without very great expense, so its 'truth' is binary, not tied to one man." Judge Madeleine Reardon had previously determined that "both brothers had sexual intercourse" with the woman "within a four-day period in the month when P was conceived," and that "it is equally likely that each of the brothers is P's father." Sir Andrew said the first twin "had no right" to be registered as the father and that any parental responsibility he gained from it "ceases to apply." However, he emphasized that nothing had convinced him to declare that the first twin is not the father. "Failure to prove a fact means it is not proven, but it does not mean the opposite is proven," he said.