someone on Komica Taiwan forum post this on the Yugioh discussion thread out of random
and showed a scan of this month's vjump, feature the final member of the Royal Knights.
There were total of 12 Royal Knights, but not all of them were revealed, then in X-evolution, Alphamon's appearance as the 13th Royal Knights.
So year by years they have been revealed more
And now they finally revealed the 12th Royal Knights: Jesmon