Why Send Barristan To Daenerys Not Aegon/Young Griff

Ser Barristan The Bold Selmy is considered one of the most honorable men in the seven kingdoms of Westeros and the most well known kingsguard knight. When he shows up to Varys and Illyrio they don't choose to send him to their favored candidate for the throne. Aegon aka Young griff, who needs symbols of legitimacy as much as anyone could. They instead send him to Daenerys Targaryen instead... so why? Well it turns out there is a very good reason.