A system for treating a body vessel, the system comprising: a delivery device having a proximal end and a distal end and a prosthesis retained on the delivery device; the prosthesis comprising: a main body comprising a proximal end, a distal end, and a lumen extending from the proximal end to the distal end of the main body; a first leg extending from the main body and comprising a proximal end, a distal end, and a lumen extending from the proximal end to the distal end of the first leg and in fluid communication with the lumen of the main body; and a second leg extending from the main body and comprising a tubular graft body comprising a proximal end and a distal end, the second leg comprising a stent attached to the graft body; the prosthesis being loaded in a predeployment configuration in the delivery device in which the graft body of the second leg is inverted into and positioned within the lumen of the first leg, and the stent of the second leg is positioned outside of the inverted graft body of the second leg and in which the proximal end of the main body is oriented towards the proximal direction and the first and second legs are distal of the main body; and the prosthesis having a deployed configuration in which the second leg extends outward from the main body, the graft body of the second leg comprises a lumen extending from the proximal end to the distal end of the graft body of the second leg and in fluid communication with the lumen of the main body, the stent of the second leg is positioned within the lumen of the graft body of the second leg, and in which the proximal end of the main body is oriented towards the proximal direction and the first and second legs are distal of the main body a delivery device having a proximal end and a distal end and a prosthesis retained on the delivery device; a main body comprising a proximal end, a distal end, and a lumen extending from the proximal end to the distal end of the main body; a first leg extending from the main body and comprising a proximal end, a distal end, and a lumen extending from the proximal end to the distal end of the first leg and in fluid communication with the lumen of the main body; and a second leg extending from the main body and comprising a tubular graft body comprising a proximal end and a distal end, the second leg comprising a stent attached to the graft body; the prosthesis being loaded in a predeployment configuration in the delivery device in which the graft body of the second leg is inverted into and positioned within the lumen of the first leg, and the stent of the second leg is positioned outside of the inverted graft body of the second leg and in which the proximal end of the main body is oriented towards the proximal direction and the first and second legs are distal of the main body; and the prosthesis having a deployed configuration in which the second leg extends outward from the main body, the graft body of the second leg comprises a lumen extending from the proximal end to the distal end of the graft body of the second leg and in fluid communication with the lumen of the main body, the stent of the second leg is positioned within the lumen of the graft body of the second leg, and in which the proximal end of the main body is oriented towards the proximal direction and the first and second legs are distal of the main body