Gerard de Sede, in a remarkable book called La Race febuleuse, claims that the Merovingians were descended from matings between extraterrestrials from Sirius and the Tribe of Benjamin in ancient Israel, and other notions about them are equally remarkable.
For instance, the semi-legendary founder of the dynasty, Merovech, allegedly sprang from a union of a woman with a sea-creature.
There are also claims that this family is linked back to another extraterrestrial race of Serpentine peoples.
I've also read in some places that the Merovingian's were thought to be direct descendants of Jesus Christ and Mary Magdalene. And others disagree saying that they possessed the blood of demonic entities. Many of the Merovingians died under mysterious circumstances.
More or less, the Merovingians do exist historically, just with a great deal of mystique surrounding their family name.