The Internet lit up with excitement earlier this week, when David Tennant and Catherine Tate, a.k.a. the Tenth Doctor and Donna Noble, announced they would be re-uniting for new audio Doctor Who adventures for production company Big Finish. Though they’ve long produced audio versions of the Classic Who era, Big Finish has only now attained the rights to the New Who adventures. There are several upcoming New Who chapters to explore, including some with John Hurt’s War Doctor. But it’s the Tenth Doctor and Donna Noble that have kicked up the most excitement, and David Tennant has a good idea why.

“The end of [Donna’s] story is deeply tragic and that adds to the legend, I think, and brilliantly captured by Catherine Tate,” Tennant told Vanity Fair during a recent phone call. He’s referencing the fact that, while the other primary companions of the New Who era—Rose (Billie Piper), Martha (Freema Agyeman), Amy (Karen Gillan), and Rory (Arthur Darvill)—all got some form of a happy ending when they left the TARDIS, Donna’s end was a heartbreaker. Rose got to live happily ever after with her knock-off Doctor, Rory and Amy got to grow old together, and Martha, well, she got to marry Mickey (Noel Clarke). But while Donna’s story also ended with a wedding, it’s also one the saddest final acts for a Doctor Who companion. Thanks to her adventures with the Doctor, Donna went from flighty temp to “the Doctor Donna,” one of a very few times in the modern era we’ve come close to getting a female Doctor in the TARDIS.

But thanks to a quirk in the mythology, in order to save her life, the Doctor had to wipe Donna’s memory of any interaction with him. She went back to her superficial life without any memory of what she had accomplished. It was crushing for everyone who had grown to love Donna. Tennant says, “I think that’s why people feel so fondly towards Donna. So it’s a rare treat and so important that we get to experience more of her in these new stories.”

The Doctor and Donna will re-unite for three adventures that pre-date her tragic ending, so we’ll get to see Ten’s best friend back in fighting trim. Tennant says he and Tate “enjoyed a few days in the studio revisiting those characters in three different stories, which will be available on CD in the New Year. And download of course, of course. On CD makes me sound like some sort of prehistoric dinosaur. It will exist in all the digital formats that one might expect. But yeah, it was lovely to revisit that part of my life, which is almost 10 years on now.”