Retail tycoon Philip Green promised to help fix a gaping hole in the pension scheme of BHS as he fielded questions from UK politicians over the demise of the department store chain he owned for 15 years.
BHS collapsed into administration in April, little more than a year after Green sold it to Dominic Chappell for a nominal sum.
This will result in the likely loss of 11,000 jobs as the chain is wound down.
Chappell was a serial bankrupt with no retail experience.
The collapse has left BHS's pension fund with a deficit of £571m and tarnished the Topshop-owner Green's reputation as a leading British businessman.
Under questioning from UK committee members, Green apologised for what happened to BHS and said he was working on a plan to plug the pension deficit, calling the situation "resolvable, sortable".
Asked about the sale of loss-making BHS to Retail Acquisitions Ltd, a little known vehicle led by Chappell, for £1 in March 2015, the billionaire admitted it was a mistake.
"Unfortunately we found the wrong guy," he said, adding: "Would I do that deal again? No. Am I sorry we did it? Yes."
But his contrition was mixed with flashes of annoyance as he was probed more deeply. He frequently interrupted committee members and complained about the line of questioning.
Green said he had trusted Chappell as a buyer because he had been approved by Green's adviser Goldman Sachs, and was being represented by law firm Olswang and financial adviser Grant Thornton, names he called "reputable, well-regarded".
Green did not provide details on the plan he is working on with Deloitte to plug the pension deficit - a figure based on how much it would cost to address the shortfall between assets and future liabilities with either insurance or a buyout - as he sought to reassure BHS's 20,000 pension-holders.
"We will sort it, we will find a solution," he said.
He told UK lawmakers the plan would offer BHS pensioners a "better outcome" than compensation available from the Pension Protection Fund, the levy-funded UK lifeboat scheme that helps finance pensions after company insolvencies.
The pension deficit compares to the £423m of dividends Green paid out during his ownership of BHS from 2000-2015, mainly to his family.
For nearly two decades, Green has been one of the leading figures in Britain's retail sector, buying Topshop owner Arcadia in 2002, and twice trying and failing to buy Marks & Spencer, Britain's biggest clothing retailer.
Chappell last week told lawmakers he accepted partial responsibility for the collapse of 88-year-old BHS, which had 164 stores, but said Green and the retailer's management should share the blame.
The UK's Insolvency Service and the Pensions Regulator are also investigating BHS collapse.
