bro on page 410 will says at the bottom i am 1 of 4 demigods who has been to tartarus refering to Percy, annabeth, nico and him but wasn't Lester Papadopoulos a demigod because he could consume amarsoda and necter and not die.
also he was Tartarus because the gods could not see him and only demigods can go to tartarus because hades says in greek heros that only gods and demigod can enter tartarus