Originally, I thought Merlin, Lancelot, Guinevere, Morgan le Fay and Mordred were the only people who knew Arturia was female when she was king.
While reading up on Kay's profile on the Wikia, I read that he knew she was a female and vowed to keep it a secret
Her identity as being female was known to him, but he kept the secret all his life after being sworn to secrecy by Merlin.
So this got me wondering: Was there anyone else who knew that King Arturia was in fact a woman? How did they find out?