Love her or hate her, it is important to note that Melisandre has played a very pivotal role in the Game of Thrones. Her advice and her arcane abilities have been, for the most part, useful to Stannis Baratheon -- until the end, that is.
It is no surprise that other followers of the Red God would eventually end up popping into positions of influence in this brutal world. So far, we have have seen the Red Priest Thoros of Myr and his resurrection abilities, as well as a brief appearance of an unnamed Priestess in Volantis.
Now, we are going to meet an important follower who will end up advising Tyrion in his efforts to run the city-state of Mereen after Daenerys' dragon flight. She will be played by British actress Melanie Liburd who has previously appeared in Strike Back and Dracula.
A brief video of her audition has surfaced online. In it, she is referred to as a High Priestess named Kinvara -- which means that she outranks Melisandre and may very well be her boss!
This is, of course, a departure from the book where the High Priest was a man named Benerro. Tyrion was also accompanied by a Red Priest named Moqorro on his journey to Mereen. This new character may very well be a combination of those two charac.