What do you call a person who is a mentor to someone but he is not aware of it

Say I have a person called 'X' and he has been following every move, every mistake of 'Y' and has secretly considered him a mentor in his own mind. But 'Y' does not know about it.

One day 'X' decides to tell his secret to 'Y'.

Now how does 'X' tell 'Y' that "you've been my mentor all these years without you ever knowing it"? Is there a single word to describe it, like "you were my secret-mentor all these years" (just giving a vague idea about what I am seeking).

Consulting a thesaurus for mentor yields: adviser, coach, guide, instructor, teacher, trainer, tutor, and counselor. None of these seem to work.

Consider role model:

a person whose behavior, example, or success is or can be emulated by others, especially by younger people.

Unlike mentor, this word does not suggest that the person in question is aware that they are acting as such. In fact, people (for example, celebrities) are often role models for children without their ever knowing it.