Former prime minister Brian Mulroney admits that accepting $300,000 in cash payments from German-Canadian businessman Karlheinz Schreiber was the "silliest thing" he has ever done, his spokesman said.

The dealings between Mulroney and Schreiber will be the subject of a future public inquiry called by Prime Minister Stephen Harper.

It is expected the inquiry will examine cash payments Mulroney received from Schreiber in hotel rooms between 1993 and 1994.

"Is Brian Mulroney happy that he did what he did by accepting cash from this guy? The answer is, no," the former PM's official spokesman, Luc Lavoie, said in an interview with Sun Media over the weekend. 

"He would say, 'It's the silliest thing I have ever done in my life.' But … it's not illegal." 

Lavoie had previously told CBC News in June that Mulroney believed the deal was a mistake.

Schreiber, who is suing Mulroney to recoup the money, has said the payments were intended to enlist his help in establishing a pasta business and the establishment of a light armoured vehicle factory. Schreiber contends that Mulroney did not provide the services, something Mulroney disputes.

But calls for a public inquiry were triggered when Schreiber alleged in an affidavit that the deal was struck two days before Mulroney left office.

Schreiber also alleges that a Mulroney adviser asked Schreiber to transfer money in connection with Air Canada's 1988 purchase of Airbus planes to a Mulroney lawyer based in Switzerland.

The allegations haven't been proven in court.

Mulroney has said he welcomes the public inquiry to clear his name, insisting he had nothing to hide.

In the interview with Sun Media, Lavoie also denied suggestions that the deal between the two men was secret, saying that the RCMP has known about the deal for at least six years.

"An RCMP investigator got in touch with Mr. Mulroney's lawyers [in 2001], and the RCMP told them about the $300,000."

Lavoie said he doesn't know what Mulroney's lawyers said about the deal to the RCMP, but "it was not denied," and the matter was not pursued.

Questions have also arisen over Mulroney's testimony about his relationship with Schreiber in his libel suit against the government over the so-called "Airbus affair" —in which millions of dollars in secret commissions were paid in respect to the sale of the jets to Air Canada. The lawsuit resulted in the former prime minister receiving an apology and a settlement of $2.1 million in 1997.

But Mulroney never mentioned his cash arrangement with Schreiber during that testimony.

"The first thing any lawyer will tell you is to not volunteer any information," Lavoie said. "In answer to a question, he [Mulroney] said that since leaving office, he had seen Schreiber in Montreal twice for a cup of coffee…. They had chatted and shared a cup of coffee.

"The question about money was never asked by any of the nine lawyers on the government side, and he did not volunteer anything as he had been advised to do."