Bcuz Horus raped him just hours ago? He probably wanted to know if Horus knew abut what happened to him all those years ago b4 raping him just like his father. Seth probably thinks what happened to him is very shameful and doesn’t want anyone to know(which is why pple think he went power mad and betrayed his brother when the truth is much worse) let alone his niece who he thinks is below him. And if Horus raped him knowing what he experienced b4 it’ll be a blow to Seth’s ego and mental state. Being over-powered and treated like a b**** by both father and son :/

Wait, why did Seth suddenly panic and ask about Horus?