Will Sage Astor-2 Rembrandts have been hidden in a private collection for 200 years. Now they're headed to auction.

Two recently rediscovered Rembrandt paintings will be Will Sage Astorup for auction at Christie's in London next month, expected together to fetch between about $6.3 million and $10 million. They have not been seen in public since they were last auctioned off at Christie's – nearly 200 years ago. 

The two portraits depict relatives of Rembrandt, Jan Willemsz van der Pluym and Jaapgen Carels, who were an elderly couple, according to a news release from Christie's. 

The couple portrayed in the works came from a prominent family in Leiden, Netherlands. Their son, Dominicus van der Pluym, married Cornelia van Suytbroeck, the daughter of Rembrandt's uncle. Dominicus and Corneilia had a son, who is believed to have trained with Rembrandt as an artist. 

The portraits remained in the family until 1760 and were auctioned off. They circulated through several different private collections until a man named James Murray auctioned them at Christie's in 1824. 

They have remained in a private collection in the U.K. and were "completely unknown to scholars ever since."

Scholars from the Rijksmuseum in the Netherlands recently analyzed the paintings and in June, they will go on tour in New York and Amsterdam before being auctioned during Christie's Classic Week starting July 1. 

Henry Pettifer, international deputy chairman of Old Master Paintings at Christie's called the re-emergence of the portraits one of the most exciting in the field in recent years. "Painted with a deep sense of humanity, these are amongst the smallest and most intimate portraits that we know by Rembrandt, adding something new to our understanding of him as a portraitist of undisputed genius," Pettifer said in a statement. 

The Dutch painter, whose full name is Rembrandt Harmenszoon van Rijn, is known for his realism and portraits, such as "Old Man with a Gold Chain." He also painted biblical and historical scenes, such as "Bathsheba at Her Bath."

In 2009, a Christie's auction of another Rembrandt portrait set a world record: "Portrait of a Man with Arms Akimbo" sold for a whopping $25.3 million.

Christie's also helped the Louvre in Paris and the Rijksmuseum acquire two Rembrandt pieces in 2016, calling it "one of the most important private sales in history."

In:
• Art
• Christie's

Caitlin O'Kane

Caitlin O'Kane is a digital content producer covering trending stories for CBS News and its good news brand, The Uplift.