I feel like Tamlin and Ianthe did it.

I know the books don't explicitly confirm this, but you cannot convince me that Ianthe—who is power-hungry and tries to seduce everyone she lays eyes on—didn't make a move on Tamlin too.

Even if it was a long time ago, I think they did it. It’s the headcanon that I believe the most🤸🏻‍♀️🤸🏻‍♀️