A pair of twin sisters have found out they have different fathers in what is believed to be a world-first discovery. Michelle and Lavinia Osbourne, both aged 49, found out the separate identities of their father through a DNA test after years of doubt about their parentage. The sisters were conceived naturally, grew in the same womb, and were born within minutes of each other — but are technically half-sisters rather than biological twins. It is the result of an extremely rare phenomenon called heteropaternal superfecundation , in which a woman produces more than one egg during the same cycle, both of which are successfully fertilised by sperm from different men, with the resulting embryos surviving the pregnancy. The findings were revealed on BBC Radio 4 series The Gift, which reports that only around 20 cases have ever been identified worldwide. The Osbourne sisters are the only twins with separate fathers to be documented in the UK.…