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By Robert Frank

A tennis ball-size diamond failed to sell at a Sotheby's auction in London on Wednesday, perhaps the result of Brexit jitters.

The highest bid for the uncut 1,109-carat Lesedi La Rona stone was $61 million, below the minimum reserve price. Sotheby's had estimated the diamond would sell for $70 million, which would have made it the most expensive ever sold at auction.

"Sadly, Lesedi La Rona was not sold but it is a magnificent stone and it will go down in history as one of the greatest stones ever discovered," Sotheby's said in a statement.

Read More from CNBC: Largest Uncut Diamond Heads to Auction in Break With Tradition

The record for an auctioned diamond was reached last month, when the 14.62-carat Oppenheimer Blue sold for $57.5 million at Christie's.

The Lesedi La Rona is about the size of a tennis ball. When it was was unearthed in November from Lucara Diamond's Karowe mine in Botswana, it became the largest diamond discovered in more 100 years and the second-largest ever.

Its sale would have been unusual because it involved a raw diamond rather than a cut stone. Typically, a diamond miner would have the stone cut before a sale.

Read More from CNBC: London Art Auctions May Be a Bargain for Savvy Buyers

But Canada-based Lucara Diamond wanted to sell the diamond directly to a wealthy buyer to capitalize on the current boom in gem prices. That includes the sale of the Oppenheimer Blue in May, and a 15.38-carat pink diamond that went for a record $31.6 million a day prior.

That bet, however, did not pay off. Stocks and financial assets have been volatile, especially after last week's Brexit vote.

Ahead of the auction, Sotheby's David Bennett called the diamond a "find of a lifetime."