I wanted to clarify a few misconceptions about Matthias and the Saint Johns.
First, there really is no TRUE Saint John family of England. There are many branches of Saint Johns that go through Britannia. DNA testing has bestowed upon us many varied lines of possibilities. It is a very confusing lot to deal with Matthias not withstanding.
The only effective question revolves around his origins, of which we are not 100% certain. I will say this though, I am confident that he is a descendant of Richard Saint John, who was a brother to Oliver Saint John (who was NOT the Dark Lanthorn) There is some compelling evidence that suggests a relationship, for example, Matthias twin brother and sister, Nicholas and Elizabeth, who would be the children of Richard, bear the same exact names as their grandparents, Nicholas and Elizabeth Saint John. Nicholas and Elizabeth always lived in the same towns as Matthias, and I think are both buried in Norwalk (but not together)
There is some other paper evidence which points toward a link to Richard with Matthias. This lineage would be tied in to the "Aristocratic" lineages of Norman descent. However, we must also consider some scientific issues that come with dna testing. There are reportedly several "npe", or non-paternal events. To clarify, out of wedlock births or adoptions. These were quite common throughout history, even today, where there might be a hiccup and someone is born into a family but was not created by the husband, but still bore the surname. This would create the illusion of an established relationship, and for all practical sociological purposes would qualify, but when comparing dna values, you would see a negative match for kinship. We would need to find the remains of the progenitor of that line (Hugh DePort) and work from there to have an abstract of absolute scientific relationship. The possibilities are somewhat endless from a permutative aspect, because we are discussing 13 generations to Matthias and close to 60 generations back to Hugh, the progenitor. Keep in mind that the surname of "De St. John" was assumed by a male from his bride. In other words, a DePort assumed the surname of his bride, De St. John, and this is how that aristocratic line began.