Tennant is returning to the show as a new incarnation of The Doctor for three special episodes to mark Who's 60th anniversary, having regenerated from Jodie Whittaker's Thirteenth Doctor during her final episode last year.
The show has a history of producing exclusive scenes for the CIN telethon and this year's mini-episode will see Juice actor Rizwan appear as a mysterious character called Mr Castavillian.
In the story, written by showrunner Russell T Davies, The Doctor will 'uncover an age old mystery involving one of the his oldest foes', with publicity pictures suggesting that it could involve The Daleks.
"It was such an unbelievable joy to work with my Whoniverse idols David Tennant and Russell T Davies," said Rizwan, who has previously written for shows including Sex Education. "My inner child was losing his mind on set."
"Every year that I was on Doctor Who we did something for BBC Children in Need, so it only feels right to be doing something this year," said Tennant.
"Children in Need is a national tradition, it's certainly a BBC tradition and Doctor Who is part of that. I'm so glad we're able to give Children in Need viewers this little extra treat."
Davies added: "Doctor Who has a fine tradition of supporting BBC Children in Need, and I hope that fans and new viewers alike will be able to watch, enjoy, and contribute to this wonderful cause."
Children In Need airs Friday from 7pm on BBC One, while Doctor Who returns for the first of its three specials on Saturday, November 25.