The names Titania and Mab both come to us from Shakespeare, through A Midsummer Night's Dream and Romeo and Juliet, respectively. Both are described as queen of the faeries and the consort of Oberon, the king.
This led Orson Scott Card to write an urban fantasy novel (whose name I can't remember at the moment) in which the queen was a major character, and Mab and Titania were two different names for her, and the plot had to do with Oberon doing something problematic. This is all reasonable enough if you accept Shakespeare as authoritative on this aspect of mythology.
Jim Butcher, on the other hand, took a very different approach: there are two Faerie Courts, each with its own distinct queen. In the Dresden-verse, Butcher always seems to adhere pretty faithfully to source material for various myths, and find interesting ways to update them and make them seem to work in the modern world. Which brings us to Mab and Titania, who are both supposed to be the consort of Oberon.
Who is Oberon in the Dresden Files? I don't believe he's ever actually been mentioned in any of the books, and the obvious answer here--a polygamous situation involving the two queens--is... well... if you've read the books you know there's simply no way that could possibly be stable.
Has the author ever said anything about Oberon and his role in-universe?