From
Transactions1:
The Selwyns of Gloucestershire are said to be an elder branch of the Selwyns who were settled at Friston. in Sussex, during the 16th and 17th centuries, and to have come into this county about the time of Richard III [1480s].
The text then continues with a brief summary of the Sussex Selwyns and a hypothesis of the connection (being John Selwyn, son of Thomas Selwyn and Agnes Bates, who is said to have fled Sussex and settled in Gloucestershire).
Footnotes
[1] Transactions of the Bristol & Gloucestershire Archaelogical Society, 1877-1878, Vol. 2, pages 241-284