Dracule was told by the real Dominus to lie to the other Dominus about the truth about his mother, and he did. But he didn't expect Dominus to catch the truth he wanted to keep hidden forever.
It wasn't his intention to hide it, but that was his mother's wish. His mother didn't want him to know his father.
"When?" He asked and Dominus understood his question.
"Two to five years ago, I think. I had my doubts for a long time. You've always appeared beside me when I'm down, sick, or in tears, there's no way that's possible without a bond. My reckoning was clarified when I saw the missing part of my mother's book hidden under bunches of books on the shelf, it revealed attempted burns." He shrugged as if I was nothing. "And my eyes. Your eyes are golden, but I've seen a mixture of red in them. No one has such eyes except you."
"You are supposed to know this, forget everything and live."
"You cannot compel me, Father,"
"Stop calling me that-"