Exactly, and he can’t act as POTUS until he is “qualified”.
Article II does not distinguish between ineligibility prior to an election or after. If after “acting as president” it is determined that the person fails to meet Constitutional requirements they are legally disqualified and removed.
“No person except a natural born citizen, or a citizen of the United States, at the time of the adoption of this Constitution, shall be eligible to the office of President;”
“Shall be eligible” is a mandatory imperative. A person who is not a natural born citizen can not ever be president.
“neither shall any person be eligible to that office who shall not have attained to the age of thirty-five years, and been fourteen Years a resident within the United States.”
A person who is not 35 years old and 14 years a resident can not ever be president.