Final answer:
Hamlet disclosed the existence of the ghost to Horatio, as evidenced by a line from William Shakespeare's play Hamlet, seeking to confirm and validate his supernatural encounters.
Step-by-step explanation:
Hamlet revealed the secret of the ghost to his friend Horatio.
The line from the play Hamlet by William Shakespeare that serves as evidence is: "Horatio says 'tis but our fantasy, And will not let belief take hold of him Touching this dreaded sight, twice seen of us. Therefore I have entreated him along With us to watch the minutes of this night, That if again this apparition come He may approve our eyes and speak to it" (from 1.1 of Hamlet).
This exchange between Hamlet and Horatio not only serves to confirm the existence of the ghost to Horatio but also seeks validation of Hamlet's own experiences with the supernatural. The literary analysis of this encounter further explores themes such as the oppression of Catholics during Shakespeare's time and the reliability of Hamlet as a narrator within the story.