The final piece of what were once called "toxic waste" loans the federal government needed to sell has found a buyer.

Santander Bank, the Boston-based subsidiary of Spanish financial giant Banco Santander, has acquired a 20% equity stake in a $9B portfolio of loans from the failed Signature Bank, the Federal Deposit Insurance Corp. announced Wednesday.

Santander paid $1.1B for its stake in the portfolio, which is entirely backed by rent-stabilized and rent-controlled housing, the FDIC said. Santander's purchase brings to an end the FDIC's auction of the $33B of commercial real estate loans it seized when Signature failed in March.

Signature had been one of the most prolific lenders to commercial real estate in New York City, and its failure continues to have ripple effects throughout the industry.

In the days after Signature's failure, which was triggered by the run on Silicon Valley Bank the day prior, Flagstar Bank acquired its deposits and branches but rejected Signature's CRE loans.

Selling those loans was seen as a far more difficult task, as plummeting transaction volumes has made it more challenging for deal-makers to agree on real estate values. Signature hired Newmark to market the portfolio, which was broken into parts and opened up for auction in September.

A 20% stake in the largest slice of the portfolio — $16.8B in office, retail and market-rate multifamily loans — was sold to a venture of Blackstone, Canada Pension Plan Investment Board and Rialto Capital last week for $1.2B. A day later, the FDIC announced that Related Fund Management, Community Preservation Corp. and Neighborhood Restore Housing Development Fund Corp. acquired a 5% stake in a $5.8B rent-stabilized portfolio for $171M.

Santander's purchase of the remaining $9B — which was broken into three pools, according to the bank — allows the FDIC to turn the page on the major banking collapses of 2023. While the FDIC retains majority interests in each of the loan pools, the buyers will take over managing the assets as long as they meet the conditions of the purchases.

A Newmark team led by Doug Harmon and Adam Spies acted as the financial adviser for the FDIC.

UPDATE, DEC. 21, 1:30 P.M. ET: This story has been updated to include Newmark's role advising on the loan sales.