Ontario's integrity commissioner confirmed Monday he is investigating a complaint against former Progressive Conservative leader Patrick Brown.

Integrity commissioner J. David Wake confirmed the probe in a statement to media early Monday afternoon.

The complaint was made last week by PC MPP Randy Hillier, questioning how Brown could afford the mortgage on his $2.3 million house and alleging Brown violated the rules for MPPs by failing to declare all his sources of income.

Hillier also questioned how Brown paid for overseas trips, including travel with his girlfriend, who was a Queen's Park intern at the time. In his complaint, Hillier suggested some business people may have covered trip costs.

If Brown, his office or the PC party did not pay for the travel, failing to disclose a sponsor would breach integrity rules.

In response to Hillier's complaint last week, Brown called the allegations "imaginary" and "make-believe."

In a statement he posted to Twitter, Brown called the allegations "either entirely fictional, constituting defamatory baseless allegations … or statements of fact that are both true and perfectly acceptable."

On the questions about his mortgage and income, Brown said he spent approximately $90,000 of his annual $120,000 after-tax income on the mortgage, and lived off the rest.

On the complaint about his travel, Brown said it's "simply false" that he accepted a gift of travel. He called the travel "cultural outreach missions … paid for by the PC Party, approved by the PC Ontario Fund."

Brown's spokesperson tweeted Monday that a statement would be coming soon. It was unclear whether it would be in response to the integrity commissioner's probe.

The investigation comes amid the race for a new PC leader after Brown stepped down as a result of allegations of sexual misconduct.

Brown himself is one of five candidates seeking the top job. The others are Christine Elliott, Doug Ford, Caroline Mulroney and Tanya Granic Allen.

PC members will vote for their party's new leader between March 2 and 8. The winner will be announced on March 10.