Of course.
Ian certainly would not reveal anything about Azathoth's dreams to the two of them. After all, he had no desire to plunge two old men into philosophical torment.
He would only tell Dumbledore and Grindelwald what they needed to know.
It was kindness.
And caution.
After all, in the Cthulhu mythos, knowledge itself was a form of contamination.
"Those beings, we call them—the Great Old Ones." Ian chose his words carefully, speaking only of what could be said. He had already done considerable research into contamination.
At his words, Grindelwald's breathing quickened. Dumbledore fixed his gaze tightly on Ian, waiting for him to continue.
"One of the oldest, and one of the most widely known," Ian said, "is called Cthulhu. It sleeps in R'lyeh, the sunken city deep beneath the Pacific Ocean, waiting for the day the stars align. Its power can corrupt any life, twist any reality, and drag all order into eternal chaos."
He paused. A complicated emotion flashed through those deep eyes—helplessness born from having experienced something terrible. "I once faced it directly."
Ian said it casually.
Dumbledore's pupils abruptly contracted. Grindelwald's hand trembled, and his wineglass nearly slipped from his fingers.
"You... faced Cthulhu directly?" Grindelwald's voice was so hoarse it was nearly inaudible.
Ian nodded. An expression almost weathered with age, utterly unfitting for his young face, surfaced there. "During one of my journeys through time, on another timeline, Cthulhu's will tried to corrupt my world. Its dreams covered reality, and its power contaminated the entire dimension. I... fought it."
He raised a hand, and a faint, dim green glow appeared in his palm. Though weak, it carried a heart-palpitating aura, as if it could devour everything. Just one glance at it made Dumbledore and Grindelwald shudder from the depths of their souls.