Equitable Subrogation: A Shield Against Unjust Enrichment In Mortgage Priority Disputes

OVERVIEW

A recent decision from the Ontario Superior Court of Justice, Bank of Montreal v. Hossain, 2025 ONSC 3950, offers a timely reminder of the equitable doctrine of subrogation and its crucial role in resolving complex mortgage priority disputes. This case highlights how courts can intervene to ensure fairness when a lender, through no fault of their own, loses the priority they intended to secure.

The Facts

The case involved a residential property in Oshawa owned by the Hossains respondents. They initially held a first mortgage with CIBC. The Applicant, Bank of Montreal ("BMO"), provided a new loan to refinance and pay off this CIBC mortgage, with the clear intention of registering its own mortgage as a first charge on the property. However, due to the negligence or deliberate failure of the lawyer handling the transaction, the CIBC mortgage was not discharged, and the BMO mortgage was not registered in the intended first position. In the interim, the