The Eleventh Circuit has concluded that the requirements of former section 321(a) of the Immigration and Nationality Act are not met when the citizen mother re-married the non-citizen father prior to her naturalization, even though the mother naturalized before the child’s 18th birthday, and had earlier separated from the non-citizen father. Because the mother re-married the non-citizen father prior to her naturalization, not all of the elements of derivative citizenship (namely, a legal separation from the non-citizen parent) when the last element (the mother’s naturalization) took place.
The full text of Turner v. Attorney General can be found here: https://media.ca11.uscourts.gov/opinions/pub/files/202211207.pdf