First seen in the direct-to-video story Downtime, Kate-Lethbridge Stewart will be returning for the 50th Anniversary, according to the BBC.

We’re delighted to reveal that Jemma Redgrave will be returning to Doctor Who for the show’s fiftieth anniversary special. She previously appeared in 2012’s The Power of Three playing Kate Stewart, daughter of the legendary Brigadier Lethbridge-Stewart. Jemma is part of a brilliant cast that is already known to include Matt Smith and Jenna-Louise Coleman who are joined by the returning David Tennant and Billie Piper plus screen legend John Hurt and Joanna Page. Filming is underway on the special which will be a 3D spectacular shown later this year.

They also said that new news on the 50th special will be revealed 'very soon,' so stay tuned!