Bill Potts's sexuality will be revealed pretty much straightaway in her second line of dialogue when the show returns to BBC One on 15 April.
"It shouldn't be a big deal in the 21st Century. It's about time isn't it?" Pearl Mackie, who plays Bill, told the BBC.
"That representation is important, especially on a mainstream show."
She added: "It's important to say people are gay, people are black - there are also aliens in the world as well so watch out for them.
"I remember watching TV as a young mixed race girl not seeing many people who looked like me, so I think being able to visually recognise yourself on screen is important."
"[Being gay] is not the main thing that defines her character - it's something that's part of her and something that she's very happy and very comfortable with."
Gay and bisexual characters have featured in Doctor Who before, such as Captain Jack and River Song, but this is the first time the Doctor's permanent companion has been openly gay. Although Captain Jack - played by John Barrowman - travelled with the Doctor for a number of episodes, he was not a full-time companion in the traditional sense.
http://www.bbc.com/news/entertainment-arts-39444025
I think this might be a really good season