Retired Colonel Dorcha Lee believes there should be fresh thinking on Scottish-Irish relations if there is a break with the UK, and closer ties between them.
Col Lee also said his government should support Scotland's bid to remain in the EU, and should show "sympathy" for the idea of an independent Scotland.
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A graduate of the Irish Military College and former Irish Defense Forces Provost Marshall, Col Lee also served as Director of Military Police and represented Ireland in the European Union and with UN Peacekeeping operations.
He outlined his views in a letter to the Irish Times, saying: "Fear of the consequences of Brexit, and for Ireland-UK relations, should not paralyse fresh thinking by our leaders on Scottish Nationalists’ aspirations."
The former soldier previously compiled an article for The Herald, where he set out his views on any union between Scotland and Ireland.
Writing in September last year, he said: "The union I am suggesting would initially be cultural. It would preserve and protect the heritage of our Q-Celtic languages, Irish, Scots Gaelic and Manx, without stuffing them down the throats of our English-speaking peoples.
"It would promote tourism as one geographic area. It would be a union that slowly evolves in consensus, not just of its respective governments, but of its peoples.
"Progress towards this union should never threaten the separate national interests of our respective states."