Paperwork filed late Thursday afternoon shows the previously-undisclosed buyer of the Boston Yacht Haven marina is Northern Bank & Trust, the mortgagee on the coveted but troubled North End property.

The Commercial Wharf marina sold at bankruptcy auction last Friday for $8 million, but at the time of the auction, neither Joseph Butler, an attorney at Baron & Stadfeld who is serving as the bankruptcy estate’s court-appointed trustee, nor the marina’s auctioneers, Paul E. Saperstein Co., would identify the winning bidder.

Thursday’s bankruptcy filing asks the bankruptcy judge, Frank J. Bailey, to approve the auction sale to the bank.

Northern Bank & Trust gave the marina’s previous owner, Yovette Mumford, a $10.1 million mortgage on the 4.75-acre property in 2005. Mumford defaulted on that mortgage early this year. She had purchased the marina from Modern Continental for $11.7 million.

Fourteen bidders registered for last week’s auction, and two pushed the price from $5 million to $8 million, in $100,000 increments. By taking the property back outright, Northern Bank & Trust is saying that it is unwilling to take a multi-million-dollar loss on the property.

It may have a difficult time lining up a buyer for anywhere near that $8 million price, though. The consensus among the bidders, and the dozens of observers who turned up to watch the auction, was that any price north of $5 million would be tough to justify, given the marina’s income streams.

Under an agreement between Northern Bank & Trust and the bankruptcy trustee, the first $150,000 from the sale will go toward paying off Mumford’s unsecured creditors.

Northern Bank & Trust’s attorney could not immediately be reached for comment.