This invention relates generally to an endoluminal prosthesis, and more particularly, to a stent graft assembly and method for treating branched vessels. The assembly comprises a first prosthesis having an overall shortened length comprising a main body formed of biocompatible graft material having a tapered proximal end. A bifurcated portion extends distally from the main body. The bifurcated portion comprises a first tubular portion defining a first lumen and a second tubular portion defining a second lumen. The assembly further comprises a second prosthesis having a tubular body of biocompatible graft material with a flared distal end portion. The flared distal end portion of the second prosthesis is configured to sealingly engage with the tapered main body of the first prosthesis.