According to the Swedish Tax Agency (Skatteverket), no name change was requested by the Princess or her husband-to-be in official documents filed recently certifying there is no impediment to their marriage
"Neither of the future spouses is going to change their name," the agency's Ingegerd Widell told the Aftonbladet newspaper.
She added that the Tax Agency had yet to make a formal ruling on the matter, explaining that a decision can only be taken after the two are actually married.
Royal Court spokesman Bertil Ternert refused to comment on the information.
"That's the princess's decision. I can't say anything about it," he told the newspaper.
Throughout her life, Madeleine Thérèse Amelie Josephine has been called Princess Madeleine and has never used a last name.
By refusing to take O'Neill as her last name, she can continue to be called Her Royal Highness.
According to royal expert Sten Hedman, the princess's decision was unusual among royalty.
"It might be a way to signify a presence in Sweden. She wants to show that she's a Swedish princess," he told the Expressen newspaper.