Students at St Albans High School were surprised to encounter two identical headmistresses in assembly.

Headmistress Jenny Brown launched the school’s celebration of National Science Week by explaining the science behind the statistical anomaly of identical twins.

“As an identical twin” she said, “I was formed from one zygote which split very early on in pregnancy. The zygote became two separate embryos, which had the same genetic pattern.”

She went on to discuss why identical twins interest scientists and psychologists, and ran through a number questions she is usually asked about being a twin.

As the assembly drew to a close, Jenny’s sister Jane Brown appeared at the back of the assembly hall, dressed in an identical outfit to her sister. Jane Brown, headmistress of Wimbledon High School, finished her sister’s sentences before discussing other aspects of twindom.

“They left us with an interesting question,” said sixth former Isabelle Blain, “Which one is the evil twin?”