Scottish Conservative Party leader Ruth Davidson attacked Boris Johnson during the EU referendum debate – calling into question his patriotism.
Mr Johnson criticised the European troops' failure to stop the massacres during the Balkans wars which left 140,000 people dead and many more displaced.
Appearing on a BBC referendum debate panel, the Brexit-backing former London mayor said the killing only halted and peace was brokered when an American-led Nato force "asserted its primacy".
But his comments were quickly rounded upon by fellow Conservative Party politician and Remain campaigner Ms Davidson, who served as a signaller in the Territorial Army and spent time in Kosovo as a reporter.
She said: "I think Boris maybe misjudged this panel by talking about the Balkans because what he probably doesn't know is that I was sent to the Balkans at the end of the Kosovo war as a reporter and I have never been more proud of being British in my life than watching British troops with a union jack on their arms, believing in something, pulling their weight, and helping in the European Union.
"That's what caused me to join up and serve. I think I am the only one on this panel that has ever worn the Queen's uniform."
She said that while she had deep respect for military figures like Field Marshal Lord Guthrie, the former Chief of the Defence Staff, who backs Brexit, current military chiefs are united in opposing it.
She said: "While I have the greatest of respect for retired general Lord Guthrie, I have the greatest of respect for him, and with the greatest of respect for him I would gently remind the other side of this debate that as a retired general he is not currently in charge of the safety and security of our nation.
"And all of those people who are currently charged, every single one of them and every single one of our major allies, says we are safer within the European Union."
Her comments came after Mr Johnson warned the EU has its sights on a bigger defence role and heading towards a "United States of Europe".
He said: "I believe that the EU is going in totally the wrong direction and I think it is a great mistake for it to try to take on this defence component and for it to try to evolve into a United States of Europe in the way that it is."
He said it was "a disaster" when the EU was given the task of "trying to sort out the tragedy in the Balkans", and many people died.
He added: "It was only solved when the Americans came. I was there, I remember reporting it and saw what happened with the Dayton Accords and Nato finally asserted primacy. That was the right thing."
The tense exchange came after it was reported that Ms Davidson will declare independence from her UK party if Mr Johnson becomes leader.
There is no love lost between the pair and Ms Davidson has repeatedly criticised Eton-educated Mr Johnson, who she has depicted as out of touch.