Dramatic irony is when the audience knows more tha the character. look bad through scene 1. where is there dramatic irony in hamelt

In scene 1, Hamlet (the main character of the play) was so upset about his father's death. But then his friends tell him that they've been visited by the ghost, Hamlet plan to come tonight. Then later that night, once again ghost had come to them. The ghost wants Hamlet. His friends tried to stop him from follow the ghost but he resist to find out what the ghost want from him. Hamlet just find out that ghost is actually his father! And what's more disturbing is that Hamlet's father was murdered by his brother, King Claudius! Hamlet swears to his father that he'll get his revenge for him. Now we (the audience) know now that the ghost is really Hamlet's father who've been killed. But Horatio, Barnardo, and Marcellus don't know who the ghost really is. I hope this helps.