I had never seen him before, didn't know of his existence.

And we were the only ones who knew of their existence!

He asked her how she knew of the girl's existence.

At any rate, it would be well to know of its existence.

Few people at Time knew of the safe house's existence.

Even this country's government does not know of their existence.

Until now, he had been the third to know of its existence.

I did not know of her existence until a few years ago.

And up to now he had not even known of its existence.

If he knew of my existence, I must be high on his list.