Window mullion to interior wall transition assembly

A fire-rated building assembly, comprising:

• a first wall;
• a second wall oriented at an angle relative to the first wall, the second wall comprising:
• a plurality of studs that includes an end stud;
• at least one wallboard coupled to the plurality of studs and the end stud and having a cantilevered portion that extends beyond the end stud in a first direction away from a remainder of the plurality of studs;
• wherein the at least one wallboard has an end surface facing the first wall, the end surface spaced from the first wall to create a gap therebetween;
• a wallboard support coupled to the end stud and extending in the first direction, the wallboard support positioned between the stud and the cantilevered portion of the at least one wallboard;
• an elongated fire-rated component coupled to the at least one wallboard, the elongated fire-rated component including a profile having a first leg and a second leg defining an L-shape in cross-section, wherein the first leg is positioned along an outward-facing surface of the wallboard and the second leg is positioned along the end surface of the at least one wallboard, the component further comprises a fire-blocking material strip attached to the profile, wherein at least a portion of the elongated fire-rated component is positioned within the gap;
• wherein the wallboard support includes an abutment portion configured to contact the end surface of the at least one wallboard.