The Lord of All Ancestors did not know about the Ultimate Dao Realm; he only knew of a realm that surpassed the Ancestral Gods of the Ninefold Universe.
When Jiang Chen mentioned the Ultimate Dao Realm, the Lord of All Ancestors initially thought it was a name Jiang Chen had invented. He felt it was a good name for the realm and thus adopted it, never imagining that a realm truly existed beyond the Ancestral God realm of the Ninefold Universe.
After a brief pause, he smiled and said, "Master, it is like this: after hearing you mention certain matters concerning the Dark World, I deliberately traveled there and sought out some ancient monarchs. I asked them for some ancient texts, and that is how I came to understand this."
Chapter 1993