The Stockholms Auktionsverk expects the sale of the some 25,000 ABBA items on August 10 and 11 to fetch some 830,000 kronor ($123,000).

Among the rarities are two maxi singles that Abba recorded in Swedish but never released commercially: “Hovas Vittne”, made for their manager Stig Anderson’s 50th birthday party in 1981, of which there exist around 200 copies; and “Saang till Goerel”, a song recorded for their record company assistant Goerel Hanser’s 30th birthday in 1979, of which there are only some 50 copies.

“Hovas Vittne” has an opening bid price of 25,000 kronor, and “Saang till Goerel” 15,000 kronor.

“Those two records really stand out in the collection,” auction curator Beata af Donner said.

“The Abba Collection by Thomas Nordin”, the largest collection dedicated to the iconic disco group to be sold at auction, comprises objects collected since 1974 when Abba burst onto the international scene winning the Eurovision contest with their song “Waterloo”.

Nordin, an Abba fan who was nine at the time, has since then collected rare items and unusual merchandise from around the world, such as Abba clogs made exclusively for the American market, rare Abba soaps and dolls, a large collection of clippings and books, and original posters.

“He has fantastic books of Abba clippings from 1974 until today. Abba’s entourage didn’t collect all the clippings about the band back then so these are really unique, you can’t get these anywhere now. Everything is in chronological order,” Af Donner said.

Nordin, who says Abba’s flamboyant stage costumes inspired him to become a tailor, told newspaper Dagens Nyheter that his dream was originally to open his own Abba museum.

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“But for various reasons that didn’t happen. And it feels good to bring (the collection) to an end now, even if it feels very empty at home now, in many ways,” he said.

The quartet dominated the 1970s disco scene with their costumes, kitsch dance routines and catchy melodies such as “Voulez-Vous”, “Dancing Queen” and “Take a Chance on Me”.

They split in 1983 and have vowed they will never reunite to sing together again.