He thought so because she had inherited the blood of the founder of the nation, King Rorgis, in which dwells the ability to read the minds of others.
However, the blood's power has weakened over the years to the point that most of the current members of the royal family have lost this ability. There are a few exceptions, but most of them must have direct contact in order to read the other party's mind, otherwise it will be an inaudible whisper that they can't understand.
The few exceptions to this are the Tomboy Princess and the First Queen.
The First Queen is able to read the thoughts of the people she's seen with her own eyes.
However, reading the part of the mind that holds a person's cleverly hidden intentions is difficult, since it is possible to provide false information with enough effort. This doesn't change the fact that it's still a wonderful ability, though.
He's facing off against the Tomboy Princess though, who is said to be a 【Throwback】 that's gifted with an unusual power which is exceedingly close to that of Founder King Rorgis, who was a 【Satori Mixblood】.
It could be said that the power that is able to read the deep recesses of its target's mind merely by seeing or recognizing them was way too strong.
Because she was born with this unusual power, as well as 【God of Judgement's Divine Protection】, she was confined in a tower without taking a single step outside until she was twelve years old. The princess had no freedom, though she was carefully raised to have a very important career.
Since she was chained to others from birth, she ended up seeing both the beautiful and filthy sides of many people, and as a result she became warped.
That's why she became a tomboy and manipulated others from the shadows. Although she was a princess of the royal family, she was determined to secure her own freedom, even if it destroyed the Kingdom in the process.
For that reason, he thought that if it was the Tomboy Princess, it might be possible for her to predict the coup d'état beforehand. Although his plans were strictly hidden, the Strong Grandson came to the conclusion that it may have been possible for them to be leaked in some way.
He thought this because she meant to overturn the way things are in the Sternbild Kingdom for the sake of her own freedom, which she wanted for her own convenience.
Even though he felt irritation towards the unusual power left by her distant ancestor, the Strong Grandson earnestly made preparations to attack the Tomboy Princess's private army.