Rumors persist about the involvement of past Doctors and companions like Donna Noble in Doctor Who's 60th anniversary. First appearing in the 2006 Christmas special "The Runaway Bride", the character returned for Doctor Who's fourth season alongside David Tennant's Tenth Doctor. The two actors had great chemistry and have continued to work together and remained friends in the years since their departure from the series. They've hosted a radio show together, starred in a production of Much Ado About Nothing in London's West End, and have also done various comedy sketches together.
Rumors of Tennant and Tate's return to Doctor Who began surfacing after the return of the former showrunner, Russell T Davies, was announced in 2021. Since then, Christopher Eccleston, Matt Smith, and Peter Capaldi have also been rumored to appear in an anniversary special or miniseries. Catherine Tate is notable for currently being the only rumored returning companion. This could be a key clue to the veracity of the rumors.
Catherine Tate was recently asked about a potential return on the UK's The One Show when promoting her new movie. She asserted that she hadn't been asked to come back and joked that she was still on the same number if anyone involved in Doctor Who wanted to make her an offer to return as Donna Noble. However, as Andrew Garfield's recent PR tricks have shown, this might not mean she is not returning. Garfield repeatedly shot down rumors of his return to the role of Spider-Man so regularly that it became a running joke on social media. Garfield's denials only fed into the hype around Spider-Man: No Way Home where it was proved that he had indeed been lying in interviews. It's entirely plausible that Catherine Tate has adopted a similar strategy, at the behest of Russell T Davies.
Tate and RTD have a history of top-secret arrangements. Donna Noble's first appearance in the TARDIS at the end of "Doomsday" was a huge shock to UK audiences at the time, especially as Tate was a big deal from the success of her comedy series The Catherine Tate Show. It was because of her fame that the scene was filmed while everyone else attended the Doctor Who season 2 wrap party. When it came to Doctor Who, only David Tennant, RTD, and a handful of other people knew of Tate's involvement.
Looking back on RTD's first era of Doctor Who, he regularly told white lies during the making-of series Doctor Who Confidential. In one episode, he said he had no interest in bringing back the Master. Except, Russell was building to the renegade Timelord's return from as far back as the second season premiere "New Earth", in which he originally intended that the Face of Boe impart his "You are not alone" message. Russell T Davies, like John Nathan-Turner before him, knows how to keep Doctor Who in the public eye. It's why he called the 2009 Christmas special "The Next Doctor". The public knew David Tennant would be leaving Doctor Who and it fed into the hype and speculation around the casting of who would play the next Doctor.
Russell T Davies implicitly understands the hype around Doctor Who but also knows there are still two more episodes left of the current era. In his statement on returning to the show, Davies spoke of his love and respect for both Jodie Whittaker and Chris Chibnall. He wouldn't want to distract from the Thirteenth Doctor's swansong with the Tenth Doctor and Donna Noble. In an ideal world, their return would, like Spider-Man: No Way Home, only be confirmed when watching the anniversary special. Until then, viewers can expect Catherine Tate to continue to self-deprecatingly advertise her availability on talk shows and in convention appearances until the time is right for a reveal.