The only non-European royals will be the crown prince Naruhito of Japan and King Abdullah and Queen Rania of Jordan with their children.
The Bernadotes are through blood or marriages related to the entire pantheon of European royalty and nobility.
Madeleine has lived in New York where she works for the World Childhood Foundation, a non-profit organisation founded by her mother.
In 2010, she broke off an earlier engagement after media reports claimed that her then fiance had cheated on her.
She marries O'Neil who was born in London and holds dual American and British citizenship, according to a CV released by the royal palace.
