There are persistent legends that members of the Brandenburg or Brandenberg family in the United States are descended from nobility in the Duchy of Brandenburg. This is a space where the legends can be gathered and analyzed.
Background: Timeline of Actual History Related to Brandenburg
- About 916 Slavonic tribe of Wends settled in area of Prussia between Elbe and Havel rivers -- later became province of Brandenburg. Built town of very crude houses called Brannabor. 
- 928-929 Henry I The Fowler of Germany defeated the Havelli in Prussia, capturing Brannabor and converted it to the fortified Brannaberg, later Brandenburg.
- 1134 Albrecht the Bear became Margrave of Brandenburg and instituted reforms bringing prosperity.
- 1356 a Margrave of Brandenburg one of 7 electors of German throne. Brandenburg among first Protestant areas. 
- 1417 Sigismund, Margrave of Brandenburg, had incurred such debts fighting the Archbishop of Magdeburg that he sold Brandenburg to Hohenzollern King Frederick VI for 400,000 golden guilders.
Solomon Brandenburg's Unknown Offense
- Around 1700 a nobleman named Solomon Brandenburg began to acquire land and power, offending, however, Frederick the Great, Margrave of Prussia. Solomon was then banished and all land holdings confiscated. Solomon removed to Paris, and three sons emigrated to America via Philadelphia
Giving Offense in a Berlin Parade
The Berlin Parade Legend--Version A
"A Catholic procession was passing through the streets of the city of Berlin. This procession was headed by a distinguished Loyalist who stood in high favor with the reigning Prince of Brandenburg, who was himself a Catholic.
This was during the reign of Frederick I (1701-1740) and his son, Frederick II The Great (1740-1763).
It was expected and commanded that every man whom this procession passed should take off his hat in token of honor to the great personage, who in glittering regalia rode at the head of the procession.
Two brothers (one being Solomon) stood watching the procession. Even though the brothers were near relatives of the reigning Prince, Catholic Elector of Brandenburg Frederick the Great they were Protestants and they not only refused to take off their hats to a Catholic dignitary, but they even spoke contemptuously of him.
This was reported to their relatives. The King and Elector of Brandenburg (Prussia) was angered by their action and sent forth an edict confiscating their estate.
This act was followed by persecution and fear of loosing their heads, and the brothers fled to Holland and then sailed to America, never regaining their possessions or estate in the Province of Brandenburg.
The Berlin Parade Legend: Version B
"At the time of the Reformation, as may be seen in history, some of the Princes of the Royal House of Brandenburg became adherents to the new religion. They renounced the Cathollic faith and identified themselves strongly upon the Protestant, while others of the family held to the Mother Church, remaining Catholic....
"In about 1700 AD a Catholic procession was passing through the streets of the city of Berlin. This procession was headed by a distinguished Loyalist who stood in high favor with the reigning Prince of Brandenburg who was himself a Catholic. It was expected and commanded that every man whom this procession passed should take off his hat in token of honor to the great personage who, in glittering regalia, rode at the head of the procession. 
"Two brothers (Brandenburg), one of whom is said to have been Salomon, stood watching the procession. These brothers were near relatives of the reigning Prince Elector of Brandenburg who was Catholic, but they were Protestants. They not only refused to take off their hats to a Catholic dignitary, but they even spoke contemptuously of him. This was reported to their relatives. The Elector of Brandenburg was so angered by this action he sent forth an Edict confiscating their Estate. This act was followed by persecution until the two offending brothers fled to Holland where they lived the remaining years of their lives and where the sons of Salomon Brandenburg married and reared families of their own. They were never able to regain their possessions in the Province of Brandenburg.
"Two sons of Salomon Brandenburg, Mathias and Wilhelm Heinrich (Hanson) brought their families to America and settled in Winchester, Frederick Co., VA. Mathias moved his family to Kentucky in Clark County and had fourteen children. His son Solomon married and moved his family to...Brandenburg, Ky. 
"Later three more of Salomon's sons moved to America and settled in Winchester, Va. They were Henry, Jacob, John Martin Brandenburg."
This is the only article I have found that gets a little specific. The others - all general - say it was Matthias, son of Salomon (sometimes son of Frederich Wilhelm) who was the crown prince and had to flee.
Claiming the Legend
- Matthias Brandenburg. Some time before his death in 1807, Matthias Brandenburg "revealed" to his family that he was a member of the Royal Family of Brandenburg, Prussia (The House of Hohenzollern). He told them that he and his brothers had left a vast estate in Prussia. and gave an account of giving an offence during a procession passing through the streets of Berlin -- the account given above.  This apparently be the same Matthias named in Find A Grave: Memorial #55449050.
Analysis of the Legend
- The ruling house of the country of Brandenburg since 1414 was the Hohenzollern family. They *never* bore the name "of Brandenburg". But there were many families named Brandenburg which had no connections to the rulers of the country, as well as in all other German areas there exist many families of the same name as the country who were not of any noble origin either, e.g. Bayer in Bayern (Bavaria), Hesse in Hessen (Hesse), Wuerttemberger in Wuerttemberg or Sachs in Sachsen (Saxony). They are surnames which only indicate the geographical origin of a person, not more! 
- The famous Hohenzollern who ruled Brandenburg early became Reformed Protestants. The second major line, the Margraves of Ansbach-Bayreuth, who also belonged to the house Hohenzollern, were Protestants and integrated about 3200 Hugenots in their city of Erlangen. Only one minor line of the Hohenzollern family, living at the origin of this house in south-western Germany, the Hohenzollern in Hohenzollern-Hechingen and H.-Sigmaringen, which only in 1849 came to Prussia, remained Catholic. They never had anything to do with Brandenburg. 
- The Brandenburg Elector and later "King in Prussia", Friedrich Wilhelm (Frederick William) of Hohenzollern (not: "reigning Prince of Brandenburg"), never was catholic (I think this was mixed up with the history of the Electorate of Saxony, the elector of which Friedrich August renounced the Evangelic Protestant faith and became Catholic to become elected king of Poland by the nobility of the (Catholic) Kingdom of Poland).
- The Brandenburg electors were very tolerant rulers - especially Friedrich der Grosse (Frederick the Great) who ruled when this "story" is said to have happened - and though they were of Reformed confession, they also tolerated Catholics in their countries. This was a great exception in these centuries ("Cuius regio, eius religio" - "Whose country, whose religion")!
Fake Royal Descent
A posting on Genealogy.com  illustrates how one genealogy can be artificially grafted onto another.
He quotes from an article entitled "Yes! The Brandenburgs Were Royalty" dated May 18, 1999 which purports to be the ancestors of one Matthias Brandenburg