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Madame Vastra stepped into the bedroom just as Jenny was changing into a nightgown, tired from the day's work.
"Exquisite sight, my love," she said contentedly.
Jenny turned 'round slowly, a strange expression on her face, not one she would usually have when Vastra was in such a contented mood. "Would it ruin things between us, Ma'am, if I told you something?"
Vastra frowned. "It depends on what you wish to tell me," she replied diplomatically.
"Well…" Jenny sat down on the bed and pulled the light cloth of the nightgown closer around her. "I've got a secret, Ma'am. I figured it's time I ought to tell you."
"I've heard a lot in my time, my dear." Vastra sat down on the bed, looking at Jenny in what she hoped was a non-threatening manner.
"I don't really know how to say this properly, Ma'am. It's about me and the Doctor."
A frown wrinkled the scaly skin between Vastra's eyes. "Are you in a relationship with him?" She asked indelicately.
Jenny drew back, wrinkling her nose. "No, Ma'am! You know I never would! Though I suppose in a way you could call it a sort of relationship, but not that kind, honest!"
"Then what kind, Jenny?"
"Did he ever tell you the story of his daughter?"
"Which daughter?"
"The one who died on Messaline."
"I believe I am familiar with that story, yes," Vastra said calmly.
"Well… she is… I mean, I am…" she stumbled. "I'm her. I'm the Doctor's daughter."
Vastra had the good grace not to look quite as shocked as she felt. "Does he… know?"
Jenny shook her head. "Not yet, but I mean to tell him next time he comes 'round. So, d' you… do you mind, Ma'am? That I've kept this from you?"
"Not at all, though I can't imagine quite how you've managed it."
Jenny pulled something out from under her nightgown: the small, golden necklace she always wore. "It's a perception filter, Ma'am. It's why you've never noticed."
"Take it off?" Vastra requested.
Jenny hesitated only a moment before unclasping the necklace and placing it on the night table. She spread her hands. "So here I am, Ma'am, the real me."
She didn't look any different, Vastra noticed. "You don't look any different to me."
Jenny gently grabbed Vastra's hand and placed it on the vein in her neck, letting her feel the double heartbeat.
"So you really are a Time Lord, then?"
"No' a proper one, Ma'am, or so the Doctor said. But genetically, yes."
The hand Vastra had on Jenny's neck quickly turned into an embrace. Vastra pulled away just long enough to murmur: "You're still you enough for me," with a smile; then business resumed as usual.
Author's Note: I might continue this with Jenny revealing who she is to the Doctor, though I'm not sure whether I should.
Obviously Jenny has regenerated since the Doctor met her. I'm not sure why she would be living in the nineteenth century or why she didn't tell the Doctor about herself the first time they met.
I'm sorry if there's anything known about (nineteenth century) Jenny's past that contradicts this, but I couldn't find anything in the episodes in which they appear.
I highly doubt that this is true (t's probably just a random idea that I came up with) but I thought it slightly unusual that they would use the same name twice. Hence this story.