Would a Queen Consort be understood as able to assume that? Or, the Consort not being royal, would the position fall to someone else?
Such things are determined by Parliament through the form of laws called 'Regency Acts' - in the event of the monarch not being at least eighteen years of age, a Regent exercises the powers of the Monarch until they reach eighteen.
Parliament could technically appoint anybody to the role, but recent historical precedent has meant the appointment either goes to the first person in the line of succession who is at least twenty-one (they set the minimum age for a regency higher than the age to rule in your own right) or a living parent or grandparent of the Monarch.
Under the current Regency Act (1953) if something happened to King Charles, and Prince William, leaving Prince George as the new King, Prince Harry, as the next person over age 21, in line, would become Regent. I would expect a new Regency Act to be passed in the near future which would likely place the Princess of Wales (Katherine) ahead of Harry - this is in line with the precedent set by the 1953 Act which stated that Prince Phillip, Duke of Edinburgh, would have acted as Regent for Charles (or any of his younger siblings) until they were 18 if needed. But currently, it would be Harry until a new Act is passed. Of course, that would be a fairly apocalyptic situation.
If Queen Camilla was the grandmother of George, rather than his step-grandmother, she might have been a possible regent ahead of Harry as well, but I doubt Parliament will take that step, given there is no blood relation, and the Princess of Wales is available. It's not impossible, though.
Thanks very much. I was confused as to the possibility of a non-royal Consort as ‘regent’.