An endoluminal prosthesis system may include a main graft and an extension graft. The main graft may include a tubular main body having a sidewall, open proximal and distal ends, a lumen, and a fenestration in the sidewall. The extension graft may include a tubular extension body, and tubular first and second extension legs. Each of the first and second extension legs may extend from the extension body and include a lumen in fluid communication with the extension body lumen. The extension graft may be deployable within the main graft such that the extension body extends through the fenestration in the sidewall of the main body. Each of the first and second extension legs may extend outward away from the main graft. An auxiliary guide such as an auxiliary cannula and/or auxiliary guide wire may be preloaded in the extension graft and extend through the lumen of each of the second extension leg and the extension body.
