LONDON (AP) — A set of the first four editions of William Shakespeare's plays — dubbed the "Holy Grail of publishing" by Christie's auction house — sold Wednesday for almost 2.5 million pounds ($3.68 million).

The London sale included a previously unrecorded copy of the First Folio that fetched 1.87 million pounds ($2.75 million), well above its pre-sale estimate of 800,000 pounds to 1.2 million pounds.

The First Folio, published in 1623, collected 36 plays, 18 of which had not previously appeared in print and would otherwise have been lost.

The folio and later editions published in 1632, 1664 and 1685 were sold as individual lots but all bought by a private American collector, who joins a handful of people who own copies of all four early editions of Shakespeare.

Christie's head of books, Margaret Ford, said the buyer was "a very private person" who wished to remain anonymous.

"It is a buyer I've known for some time and I've worked with and he appreciates fantastic books, and so he understood this and the importance of these volumes from the very beginning and he's the very proud owner," she said.

Prices for the later editions ranged from 47,500 pounds for the fourth to 362,500 pounds for the third, which added one more play, "Pericles, Prince of Tyre."

Ford said it was "exhilarating" to sell the four folios in the year marking the 400th anniversary of the playwright's death.

Of 750 First Folios that were printed, 233 are recorded as having survived. The one being offered by Christie's is not on the official list.

Christie's said it and two of the other folios came from a "discreet and off-the-radar" private collection in Europe and have not been seen in public for 200 years.