I think that it probably refers to Prince Maurice, (Moritz Pfalzgraf von der Pfalz), 1621-52, the younger brother of Prince Rupert, who as Commander in the West of the Royalist forces captured Dartmouth in October 1643 and with it forty Parliamentary ships. After the Royalists surrendered in 1646 he and Prince Rupert were banished from England by order of Parliament.

Maurice returned to the Prince of Orange's army until the summer of 1648 when he joined Prince Rupert and the Prince of Wales (later Charles II) in a squadron of warships that had defected to the Royalists. In 1649, Maurice sailed with Rupert on his raids against Commonwealth shipping from a base at Kinsale in southern Ireland until their squadron was chased by Robert Blake from the Irish Sea to Lisbon and the Mediterranean. When Blake drove the brothers from the Mediterranean, they sailed to West Africa where Maurice raised his flag as Rupert's vice-admiral in a captured English ship, renamed the Defiance. With only four ships remaining, they crossed the Atlantic in 1652 to resume their privateering activities in the West Indies.

Maurice was lost at sea during a storm near the Virgin Islands in mid-September 1652. His loss deeply affected Rupert who for many years believed a persistent rumour that Maurice had survived the storm and was a prisoner of the Spaniards.

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http://bcw-project.org/biography/prince-maurice