Photo courtesy of CBRE

A Mattapan apartment complex that’s been at the heart of conversations around displacement and transit-oriented development in Mattapan will become permanently affordable housing, Boston’s mayor said Monday.

The deal for the 12-building SoMa at the T complex will bring it under ownership of a Related Beal affiliate via around $90 million in private debt, $10 million in leftover city COVID relief dollars and $1 million from a city fund for acquiring market-rate housing, Mayor Michelle Wu’s office announced.

Built as the Fairlawn Estates by the Flatley Companies in the 1960s, the 347-unit complex was bought by The DSF Group 2018 using a $42.7 million loan from CBRE Capital Markets, public records show.

The company rebranded the 15 Bismarck St. building to highlight its location along the MBTA’s Fairmount commuter rail line, and raised rents, triggering protests, organizing by tenants rights groups and tension over potential impacts of transit improvements.

“For years, Fairlawn Estates has been a pillar in our community that tenants and neighbors have organized and advocated to protect and preserve,” Mayor Michelle Wu said in a statement. “Today’s acquisition is a major step toward protecting our communities and preventing displacement in Mattapan. By securing these homes as permanently affordable, we are continuing our efforts to make Boston a home for everyone and ensuring that families can continue to live and thrive in their neighborhood without the fear of being priced out. I’m grateful to Related for their partnership on this acquisition and City Life Vida Urbana and the Fairlawn Tenants Association for their years of organizing that made today possible.”

As of noon Monday, neither a deed nor other documents were available from the Suffolk Registry of Deeds, but Wu’s office described the transaction as a sale to Related Beal, and state corporation records now list several top Related Companies executives as the principals of the LLC that owns the property. A Related Beal spokesperson was not immediately available for comment.

“Affordable housing is core to Related’s DNA, and we are thrilled to provide a more sustainable living solution in such an important, transit-oriented location in Mattapan,” Related Beal President Kimberly Sherman Stamler said in a statement provided by Wu’s office. “We are grateful to the City of Boston, the Mayor’s Office of Housing, and our financing partners for collaborating on this important opportunity that will protect hundreds of residents within the Mattapan community.”

An announcement from the mayor’s office said all 347 units in the complex would be permanently converted to deed-restricted affordable housing. Half the apartments will be reserved for households earning no more than 60 percent of the area median income (AMI), while the other half will be for households earning no more than 80 percent of AMI. The agreement with Related also includes protections for existing tenants, limiting rent increases to no more than 2 percent per year and ongoing support for households with housing vouchers, Wu’s office said.

The Acquisition Opportunity Fund has helped Boston officials midwife the acquisition of around 1,000 market-rate, “naturally occurring affordable housing” units around the city in the last few years.