This newcomer appeared out of nowhere and had been watching their battle for who knows how long, yet they hadn't sensed his presence at all.
This could only mean two things: either this person possessed a treasure that could completely conceal his presence, or he was far more powerful than both of them.
If it were the first option, the newcomer would not have dared to speak in the midst of their battle; he would have chosen to remain hidden.
On the other hand, if it were the second option, it confirmed that the newcomer was at least a Divine Emperor and not an ordinary one at that.
The black-clothed man thought of several possibilities in a few seconds. This is also the reason why he did not dare to underestimate the newcomer.