Complex sentence: Bentley is most famous for narrating the UK version of the hit reality show, "Big Brother" since it's inception and fronting continuity announcements on Channel 4, where he left in July 2011 to continue narrating the revived Big Brother on Channel 5.
Split into simpler sentences: Bentley is most famous for narrating the UK version of the hit reality show, Big Brother, since its inception. He also did other continuity announcements for Channel 4 until he left in July 2011 to continue narrating the revived Big Brother on Channel 5.