Good question, actually. Thanks for asking.

I initially kind of assumed that most people would know about it, because it is a somewhat famous one, or at least, I've read it in many places. But your question made me realise that may not be the case. So, here it is, from the top of the above Wikipedia article about him, just below the header:

[ Santayana is popularly known for aphorisms, such as "Those who cannot remember the past are condemned to repeat it" ] .

Yeah, I wondered whether that might be the one. But it's slightly different from the plus ça change, plus c'est la même chose quote, so I thought maybe you had a different one in mind. (Santayana was known for his aphorisms.)

Yes, they are two different quotes. I didn't mean to use them as equivalent. It was more like, I used both, because both were applicable in the context I used them in.