DUBLIN—Bank of Ireland on Friday agreed to buy “substantially all” of KBC’s Irish performing assets for 5 billion euros as the Belgian financial group confirmed it would become the latest lender to leave the shrinking Irish market. The two banks announced they were in talks about the deal in April, just weeks after NatWest began winding down its Ulster Bank business in the Irish Republic. The departures leave Ireland with just three retail banks. Bank of Ireland, the country’s largest bank by assets with a loan book of 77 billion euros, said it would acquire 8.8 billion euros of performing mortgages, 100 million euros of performing commercial and consumer loans, and 4.4 billion euros of deposits. A portfolio of around 300 million euros of non-performing mortgages would also be acquired as part of the transaction, the joint statement from the two banks said. “Today’s agreement with Bank of Ireland Group …