Because William made a habit of mentioning
his Royal guest in every possible conversation, he was quickly
dubbed Duke by all who knew him.
News of the Royal visit and the Regal seal
of approval caused the fame of this new watering place to spread,
and soon the visitors were flocking to the town. As their numbers
grew, Suttons son-in-law erected the Union Hotel near
the Royal Original Hotel, now known by locals as 'The Dukes
Folly', and the town began to blossom.
While the Royal visit had been an unexpected
but highly beneficial evening for the town, local legend has
it that it was another spontaneous evenings celebrations
that gave the resort the name it bears today.
In the last few years of the 18th century
it is said that a party of gentlemen were in congenial spirits,
making merry over numerous bottles of wine. Determined to perpetuate
this happy occasion, they christened the town by dashing a bottle
of port on the ground and declaring from that moment on "...
the place shall be known, not as South Hawes, but as South Port."
See William Sutton's Wikipedia page for a variation of the tale. Link