Sonequa Martin-Green was first announced as the lead on Star Trek: Discovery a few months ago by Entertainment Weekly. CBS has issued several announcements since then, several of which have contained cast lists. However, for some reason (perhaps the contract wasn't actually signed yet), they're only now officially confirming her as First Officer Michael Burnham. At least they admitted it was a poorly-kept secret. I know some networks would have pretended this was an exclusive announcement.