A letter written by the Italian explorer Christopher Columbus in 1493 that detailed his historic voyage to the New World was formally returned to Italy Wednesday.

The letter, an 8-page litany of Columbus' impressions about the people, flora and fauna of the Americas that he had sent to Spain's King Ferdinand and Queen Isabella, had been replaced at Florence's Riccardiana library with a forgery that no one noticed until a few years ago.

The original, meanwhile, had been sold to a rare book collector in Switzerland in 1990, then purchased by another collector at a Christie's auction in 1992 in New York. It was finally bequeathed to the Library of Congress in 2004 by the estate of its final owner, Italian and U.S. officials said Wednesday.

"Five hundred years later, it did the same trip (as Columbus), round-trip," Italian Culture Minister Dario Franceschini told a press conference in Rome with the U.S. ambassador by his side to announce the letter's return.

U.S. Ambassador John Phillips declined to identify the estate that gave the letter to the Library of Congress, saying the investigation was still ongoing. But U.S. officials said both the final owner and the Library acquired the letter in good faith, assuming its provenance was legitimate.

The auction price was $450,000 but police officials estimate its true value is $1.13 million.

The head of the Riccardiana library, Fulvio Stacchetti, said the letter was likely substituted with a fake in 1950-51, when the Riccardiana loaned the letter to national library authorities in Rome. He said that was the only time the document had left the Riccardiana, and that it would have been impossible for it to have been substituted with a fake while it was home because the reading room is so closely monitored.

The letter is one of about 30 authentic, reprinted copies of Columbus' original letter and is known as one of the Plannck II copies.

Carabinieri art squad officials said they determined the version that was in the Riccardiana was a fake because the print style and page size were incompatible with the original.

Fox News' Matt Dean and The Associated Press contributed to this report.