Benedict Cumberbatch has revealed that his sister Tracy Peacock, 62, has passed away after battling cancer for seven years.MORE: Benedict Cumberbatch reveals harrowing health issues while filming new Netflix movieThe Hollywood star is incredibly private about his personal life and his sibling's health battle was unknown to the public until this week.WATCH: Official trailer for Netflix's The Power of the Dog"She died of cancer," Benedict revealed. "She'd been battling it for seven