The official cause of death of former football star and actor O.J. Simpson was announced Friday by his attorney and the executor of his estate. Malcolm Lavergne, who had been Simpson’s legal representative since 2009, confirmed to Fox News that the 76-year-old died of metastatic prostate cancer. It is not clear when Simpson — who was accused of but acquitted in the 1994 double murders of his ex-wife, Nicole Brown Simpson, and her friend Ron Goldman — was first diagnosed or what methods he used to treat the debilitating and painful cancer. According to the American Cancer Society, it can take…