Herodotus doesn’t mention this, but Psammis died while still a child. How it was he came to have the son Herodotus credits him with is thus a mystery. But Psammis was succeeded by Apries, whom Herodotus declares to have been Psammietichus’s great-grandson.
Apries (588-569 BC, putting him at about a hundred and fifty years prior to H.’s writing) went to war against Nebuchadnezzer, which gets him some coverage, albeit indirectly, in the Old Testament. The war ultimately went badly for Apries: he pressed into Greek colonies to the west of Egypt, in modern-day Libya, using native Egyptian troops rather than the Greek mercenaries that had served his dynasty for generations. The war went very badly for the Egyptians, who decided that Apries had sent them off to die while holding back his Greek personal guard. The country rose in revolt, and Apries sent his right-hand man Amasis to deal with the rebel leaders.
“So what’s it going to take to end this rebellion?” Amasis asked the rebel leaders.
Their response was to put a crown on Amasis’s head. “We’re not anti-monarch,” they said. “We just want Apries out.”
Amasis liked the idea of becoming king, so threw in with the rebels. When Apries heard about this, his first thought was that the rebels had taken Amasis prisoner. He sent a courier, Patarbemis, to entreat the rebels to release Amasis.
Patarbemis’s interactions with the rebels was, to put it simply, fraught. Also there was a bit where Amasis farted in Patarbemis’s face and told Patarbemis to bear that message back to Apries. Herodotus wants us to know that when Apries had Patarbemis killed, it wasn’t because Patarbemis farted in Apries’s face. Patarbemis didn’t get the chance to fart in Apries’s face; Apries executed him as soon as the general negative drift of Amasis’s message became clear.
Apries’s execution of Patarbemis convinced everybody who heard about it and who had been on the fence that Apries wasn’t a suitable king, so Amasis amassed a sizable army of disgruntled Egyptians. Apries responded by doubling down on his army of Greek mercenaries! The two armies met at Momemphis!
(Herodotus then goes off on a tangent for several pages about the Egyptian caste system and tax structure, which I feel confident in skipping, except to observe that one caste was the interpreter caste, made up of part-Greek halfbreeds raised among the mercenaries.)
Apries and the Greek mercenaries lost this civil war: they were just too badly outnumbered. Amasis took Apries prisoner and held him in the royal palace Saies for a while, but the Egyptian people demanded a public execution, and got it.