The appearance of Ancestor Dragon was unexpected for Senior Gem Emperor.
Ancestor Dragon, as the name implied, was the ancestor to the thousands of World Dragons in the Tomb of Immortals—at the beginning, the Earth Immortals subdued the Ancestor Dragon and then they multiplied thousands of these strange groups, which then supported the entire Immortal Tombs.
The Ancestor Dragon might not have the most power, but it has an extremely special significance. If the common World Dragon was the brick and stone of the Immortal Tombs, then the Ancestor Dragon was the pillar. Through blood relationship, an Ancestor Dragon could have a lot of relationships with many World Dragons. In other words, losing an Ancestor Dragon might mean losing countless World Dragons.
Because of this, when the Immortal Tombs was built, the Ancestor Dragons became the top priority. They were hidden so well that there were only a few people who were qualified to contact them.