some facts about the real life of the man in the iron mask

It's more complicated than that. This is a pet peeve of many scientifically minded people (like myself) because it leads to a lot of big misunderstandings.

In scientific terms, a theory is not the same thing as a hypothesis. A theory is a model (or set of models) or framework that explains certain aspects of the natural world. It's based on many observations and incorporates facts, laws, predictions, and tested hypotheses that are generally accepted. Theories are more general and far reaching than hypotheses, and are well established and supported by the available evidence. A theory is a prestigious thing, not a mere guess. Think of relativity, for example.

A hypothesis is a specific testable prediction, an educated guess. It's much more narrow and specific (e.g.: "if I do x than y will happen" or "x is the cause of y"). A theory can incorporate tested hypotheses, and a hypothesis may be based on an existing theory, but a hypothesis is not in itself a theory.

However, it is true that in everyday vernacular, people often refer to hypotheses as theories. Although in science, there is no such thing as 100% certainty, in every day vernacular, a scientific theory would more closely resemble what you'd think of as a "fact". However, a "fact" in scientific terms is a single observation, a little nugget of data that is not in (much) dispute.

This leads to a lot of misunderstanding among the general public when it comes to science. For instance, when people hear "theory of evolution" they think that this means that that theory is a sort of unfounded guess as to what is going on in nature ("it's just a theory"), instead of what it really is; an extremely well supported set of models with mountains of evidence in its favor - a fact in any meaningful sense of the everyday meaning of that term.