When Harry returned from the cemetery after facing the return of Lord Voldemort, Medea felt relieved for once for having restrained herself from revealing the truth about her. If Voldemort was really back, as everyone seemed to be whispering all around her, then we would certainly be looking for her, with that very obsession he possessed since hearing of the prophecy.
Only, the person the prophecy described never even came to exist. She never existed to the world. Thirteen years ago, he had failed to find even the remotest sign of her existence in what was supposed to be her house. Now, he had no hope whatsoever to find out the truth, unless he was to accidentally walk into either her or Sirius.
Not even in her deepest fears, thus, would Medea suspect to be in any way in danger. So that when Dumbledore – after the whole matter with a fake Alastor Moody was dealt with - summoned her in his office along with Harry, she was in no way prepared for the expression written all over her brother's face, who was carefully averting her gaze. Fear, anger, realization, betrayal.
"You know" it was not a question. She gaped in shock at Harry, who didn't reply, lifting instead his gaze to meet Dumbledore's.
"So, what is it that you wished to inform me and Miss Black here about, Harry?" Dumbledore gently started, the distress from the recent occurrings evident in his. From the way his piercing blue eyes scrutinized Harry's eyes, though, Medea could tell he already knew.
"There's something more that Voldemort did in the cemetery, sir." Harry began. Of course, the rumours were true, Medea thought.
"He… he seemed surprised about something. He accessed my memories, as if he was looking for something I did not even know about" Harry finally turned to Medea with a hard glare. "Medea and I seem to be brothers. Twin brothers."
"Why did he know? How could he possibly know?" was all she could reply in a whisper, still in shock.
"How could I possibly not know!" Harry burst out, yelling in anger. "How could you never even tell me, for all these years! You knew!"
"Calm down, my dear boy" Dumbledore finally intervened, standing from his high-armchair. "I honestly must admit, I did not know either". He strode towards the window, turning his back to them. "James and Lily didn't tell anyone". It was not a question, yet Medea felt she was being urged to reply.
"No, professor. They felt it was the only way to protect me from him, and from who I was destined to be. And… " She paused, unsure how to voice the truth. "They feared I would be in danger if the Wizarding World found out about me".
Dumbledore finally turned to face them, and with slow, long paces came to stand before her chair, looking down at her through his spectacles with a grave, pensive gaze. "And they feared you would be in danger from me" he concluded.
Medea did not answer, staring down at her hands.
"You were only a child…" Dumbledore whispered.
It was Harry who broke the silence next. "What would she ever be in danger from?" every trace of anger was gone from his unsettled voice.
Medea knew that her brother was, unlike her, still unaware that any prophecies had ever been told, and did not wish for him to know so soon. She had not wished to know herself, either; but Sirius had had no choice, being the only one left to know the secret, fearing that the truth would be gone with him. Now she hoped Dumbledore would be senseful enough to protect her brother from the part of the prophecy concerning him at least.
"It is not the time nor the place that you know the full details, Harry. But it is only fair that you know why your sister has been hiding her existence from you" Medea glanced gratefully towards the old wizard "On her head has been hanging a terrible prophecy, owing to which Voldemort has been looking for her ever since. Only, nobody knew she was even born."
"Then what… what was the prophecy about?" Harry asked, finally glancing to Medea with a look mixed of concern and confusion.
"It was said that I would bring the utmost power to Lord Voldemort. It was said that he would be strengthened with my love" She finished, almost scornfully. "Obviously, whoever voiced that idiotic prophecy was very, very wrong about me".