The writer has confirmed rumours that she will depart the DC Comics title.
"On Wednesday of last week, new Batgirl editor Brian Cunningham informed me by email that I was no longer the writer of Batgirl," Simone wrote on Twitter.
"It is baffling and sad, I will probably have a statement later today or maybe tomorrow. But I want to give huge, huge thanks to the other creators in the bat-offices, and editors Bobbie Chase and @yourpallsmitty, champions all.
"And the biggest thank you of all to you guys for supporting this book so hugely and making it a commercial and critical success.
"I honestly don't have the words right now to thank you all. I'm pretty choked up and it's all gratitude, not bitterness. I am very proud of what we accomplished with Batgirl and it was an honour to get to write Barbara Gordon again. Love that dame."
She released a longer piece about her feelings regarding the departure on her Tumblr. No specific reason has yet been offered for her exit.
Simone last week denied the rumours that she was off the title.
She launched Batgirl in 2011 for the New 52 alongside The Fury of Firestorm, which she departed as co-writer after six issues.
Simone currently has no ongoing projects at DC. She has been working on the Kickstarter-funded, creator-owned Leaving Megalopolis with Secret Six collaborator Jim Calafiore.