After teasing the lingering mystery about Snoke in the two previous movies of the sequel trilogy, this was finally revealed in The Rise of Skywalker just minutes into the movie. However, when Ben Solo was just in the process of turning to the Dark Side, it seems like the Supreme Leader has already teased about being controlled.
This article contains SPOILERS for Star Wars: The Rise of Skywalker and The Rise of Kylo Ren #2.
In the second issue of The Rise of Kylo Ren, the story opens with Kylo speaking to Snoke. When the Supreme Leader told Ben that he should have a new name if he were to join the Knights, this opened a discussion about Snoke's name. However, he revealed that he was "not born Snoke," but rather he "became Snoke."
You can check out this panel via a Redditor's post here.
This line alone suggests that the Supreme Leader indirectly revealed that he was, indeed, under the control of Emperor Palpatine, and that he literally "became" Snoke. Also, based on the movie, who Kylo Ren was talking to in this part could even be one of the clones.
That being said, it isn't clear if they were trying to imply that Snoke has been indirectly talking about being a clone, but as the movie suggests, well, you could say he did become Snoke and was not born as one.
Star Wars: The Rise of Kylo Ren #2 is already on sale and The Rise of Skywalker is now showing in theaters.