During City of Ashes, their relationship becomes complicated since they are lead and tricked into believing that they are brother and sister. In result, and in an attempt to rid of his feelings for her, Jace begins to ignore her in hopes that he can get over his feelings for her. This only backfires as he notices that his feelings for her have only grown stronger despite her being his "sister". The two are then forced into sharing a kiss when Clary is tricked into consuming faerie food and kissing her being the only way to free her from the Faerie courts. The kiss quickly becomes one of great passion, much to the shock of those present for it. Later, upon realizing she loves him as well, he tries to convince Clary that it doesn't matter that they're siblings and that they can be together in secret, but the idea clearly repulses her. She tells him that they should try to act more like brother and sister, instead of lovers.