Camilla at the concert on Saturday. (Reuters)

New York, Jan. 31: An elaborate ruby and diamond necklace — with plunging décolletage to match — provided the abiding image of a visit by the Prince of Wales and the Duchess of Cornwall at the weekend to the east coast of America.

The duchess wore the dazzling piece of jewellery with a low-cut deep red velvet evening gown designed by Robinson Valentine to a white-tie gala at the Academy of Music in Philadelphia.

The American media, perhaps reflecting public sentiment, is even more prone than its British counterpart to comparing the duchess with Diana, Princess of Wales.

Many Americans still remember fondly a young Princess Diana dancing with John Travolta at the White House in 1985, and tend to trot out the incident each time the duchess crosses the Atlantic.

The prince and duchess last went to the US together in 2005, amid polls suggesting — not entirely accurately — that Americans were unmoved by the visit.

This time, they were greeted by long lines of gushing fans in Philadelphia.

The Americans, who are more used to celebrities who keep fans at arm’s length, seemed to be particularly impressed by the royal couple’s informality.

“She actually offered her hand to me,” said Debbie Lefevre, 49, who gave the duchess flowers. “I was shocked.”

The academy’s evening concert and ball — for which guests paid up to £25,000 a ticket — proved similarly successful in fostering Anglo-American relations.

“Doesn’t she look awesome?” said Edward Rendell, governor of Pennsylvania.