Stefan King cut a dashing figure in his crisp white uniform - but the Royal Australian Navy captain and Iraq veteran had a tangled love life involving a wife and three mistresses, a court-martial in Canberra heard.

King was found guilty last week of claiming nearly A$15,000 ($18,813) in allowances to which he was not entitled because his marriage, the navy concluded, was effectively over. The court heard that at the time the 48-year-old was exchanging steamy emails with a married Sydney woman, Robina Frew, and with a former lover in the UK whom he dubbed his "English Rose".

The case revolved around the 18 month-period before King and his wife, Jacqueline, also an RAN captain, divorced in mid-2011, when he was still living in the marital home in Canberra - and also around the definition of marriage.

According to the military prosecutor, Brigadier Lyn McDade, the emails demonstrated that the couple were as good as separated, and King should therefore not have claimed allowances as a spouse living away from home while stationed at Nowra, on the New South Wales south coast, where he was commanding officer of HMAS Albatross.

He argued that he still regarded the house as his home - and he received support from his ex-wife, who made a surprise appearance at the court-martial. Jacqueline King, who attended in full naval uniform, declared that it was "not in [her ex-husband's] DNA" to take "one dollar" to which he was not entitled.

King, who was fined A$13,000 and stripped of his seniority, was found guilty on seven counts of obtaining financial advantage, in three instances by deception. He has said he will appeal the verdict.

Australian media has reported it under headlines such as "An officer, if not quite a gentleman".

King's cardinal error was to use his work email account to write to Frew and his other paramours, meaning that the navy - which brought the case following a tip-off - could impound his correspondence.

Among the emails read out by McDade to a rapt court were some containing poems he had penned to Frew, whom he told: "You switch on every pleasure for me."

Giving evidence, King - who received two commendations, one for his service in Iraq - agreed that he had been "madly and deeply in love" with Frew, whom he still hoped to marry. But he said that during the period in question he and his wife "ran a home together. We had meals together. The time we spent together was normal".