Maybe the missing letter has already been found and posted but if not then perhaps it’s the letter is E?

Donald J. Trump‏Verified account @realDonaldTrump

.@FLOTUS Melania will be interviewed by @SeanHannity tonight on @FoxNews at 9:00pmE!

3:50 PM - 12 Dec 2018

https://twitter.com/realDonaldTrump/status/1073002260072935424