User blog comment:B214/Question & Answers 5/@comment-66.87.82.56-20150514164636/@comment-26209278-20150514210856

Don't think it's ever been mentioned. If there was anything from the past that gave reference to it, it hasn't been brought up. I'd say it may look something similar to what the 4 excaliburs combined looked like in the Anime.

Maybe......