A modular stent graft system and methods of assembly are disclosed. The stent graft assembly comprises a first stent graft having an interface region at its distal end and a first locking stent secured to an internal surface of the interface region. A second stent graft having an interface region at its proximal end is configured to at least partially overlap with the interface region at the distal end of the first stent graft. The second stent graft comprises a second locking stent secured to an external surface of the interface region. The first and second locking stents are configured to be engaged such that the second locking stent is nested between the first locking stent and an internal surface of the interface region of the first stent graft thereby interlocking the first and second stent grafts to each other.
