Brother Zachariah is cured by Jace's heavenly fire, he reverts to Tessa's old lover, Jem Carstairs, now a mortal and dispelled of any needs of his yin fen medication to which he had needed to live. The two happily marry sometime after Jocelyn and Luke's wedding, attended by the ghosts of Will Herondale and Jessamine Lovelace. Brother Zachariah/Jem Carstairs Zachariah is a Silent Brother who becomes the one most contacted by the Clave to solve cases regarding the New York Institute in 2007 after the Silent Brothers' massacre by Valentine. He used to be Jem Carstairs, a main character of The Infernal Devices series, who was turned into a Silent Brother to save his life as he laid dying due to running out of the yin fen medication required to sustain his life, in the process breaking his parabatai link with Will Herondale and separating him from his fiancée, Tessa Gray. He and Tessa together performed the Shadowhunter protection ritual on Clary when she was younger, thus erasing her knowledge about the Shadow World for a time. When he finds out that Jace is a descendant of Will, Zachariah becomes fiercely protective of him, especially when he is put under Jonathan Morgenstern's spell and infused with the heavenly fire. In City of Heavenly Fire, Zachariah's attempt to save Jace infuses him with the heavenly fire, which burns out his yin fen and turns him back into a mortal Jem Carstairs again. During the war he finds Emma Carstairs, a descendant of his family and protects her during the war. After the war, Jem reunites with Tessa and marries her a year after Jocelyn and Luke's wedding. He also begins to keep an eye on his distant relative, Emma Carstairs, and Tessa's descendants, the Blackthorns, in Los Angeles, and Jace Herondale. See also City of Bones City of Ashes City of Glass City of Fallen Angels City of Lost Souls City of Heavenly Fire References Mortal Instruments