TORONTO -- A high-ranking officer of the Canadian Forces has been fined $2,500 after pleading guilty to signing a document that claimed he and his Ottawa mistress were in a common-law relationship.

Lt.-Col. P.W. Fredenburg, of Toronto, who is a military landmine expert, was charged in 2008 with making a false statement in a document that was required for official purposes.

He was fined by a military court martial last July at the Lieutenant-Colonel George Taylor Denison Armoury, in Toronto. The decision was only made public this week.

Fredenburg authored a number of articles on landmines including a 1997 piece for Canadian Defence Quarterly titled "The Banning of the Anti-Personnel Landmine." He also gave talks on the subject to different military agencies.

The hearing was told that Fredenburg was posted to Ottawa in 2008 away from his family in Toronto when he began seeing a woman who also worked in the military.

"The offender carried on an extramarital affair with another member of the Canadian Forces," the hearing was told. "At her request, he signed a statutory declaration stating the two of them had been living in a common-law relationship for a period of a year."

The hearing was told Fredenburg knew this to be a false statement because he did not consider the other member to be his spouse and neither held themselves out to the public as spouses.

"I am not aware of the reason or possibly reasons why the other member requested the offender to sign the statutory declaration," said Military Judge Cmdr. P.J. Lamont. "I am told and I accept that the offender did not benefit financially from signing the false declaration."

Lamont said at the time of the incident Fredenburg was in mourning due to the loss of his father.

"I have read the performance appraisal reports for the offender," Lamont said. "They are, as counsel says, stellar."

Fredenburg was ordered to pay $500 in monthly instalments until the fine was paid.