Upon discovering that Romeo is a Montague, Juliet reacts with shock and despair. In Act 1, Scene 5 of Romeo and Juliet, she exclaims, "My only love sprung from my only hate! Too early seen unknown, and known too late!" This reaction underscores the deep conflict she faces, torn between her love for Romeo and her loyalty to her family, the Capulets, who are in a bitter feud with the Montagues.
Juliet's realization reveals the central conflict of the play—her intense, passionate love for Romeo stands in stark opposition to the expectations and enmity dictated by their families. This conflict sets the stage for the tragic events that unfold, as Juliet must navigate her feelings of love against the societal pressures and dangers posed by the longstanding feud. Her initial reaction foreshadows the struggle she will face in balancing her desires with the obligations she feels toward her family, ultimately leading to the severe consequences of their forbidden love.