IF he falsely claimed to be a citizen, then there is no waiver.
On the other hand, FRAUD/Misrepresentation is eligible for a waiver per INA 212(i) BUT it is hard to meet the eligibility criteria. He must file an I-601 and IF he was removed because of that or for ANY REASON he may also need to file an I-212. WAIVERS are not easy to get, especially for a foreign located adult son of a USC and/or LPR. So, first of all, has he got a qualifying relative? IF NOT, that is the end of the story. The qualifying relative does NOT have to be the I-130 petitioner and only his parent or spouse may be used for this (stepparents also count if they meet the INA definition for a step relationship INA 101(b)(1)(B) and 101(b)(2).
(i) (1) The Attorney General may, in the discretion of the Attorney General, waive the application of clause (i) of subsection (a)(6)(C) in the case of an immigrant who is the spouse, son, or daughter of a United States citizen or of an alien lawfully admitted for permanent residence, if it is established to the satisfaction of the Attorney General that the refusal of admission to the United States of such immigrant alien would result in extreme hardship to the citizen or lawfully resident spouse or parent of such an alien or, in the case of a VAWA self-petitioner, the alien demonstrates extreme hardship to the alien or the alien's United States citizen, lawful permanent resident, or qualified alien parent or child.