"Well as this bank (Bank of Ireland) plus Virgin money, plus our Greek investment and American banks has just gotten to be too big a portion of the portfolio so in order to avoid and undo concentration we needed to make a sale and a large sale," Ross told CNBC.
Ross said he thought Ireland and the bank had a very good future and he would "miss the association" with both.
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But he added that his company has started looking around other economies on the periphery of the euro zone.
"We did make an investment, not a terribly large one, but we did invest in Eurobank which is one of the main four banks in Greece, so I don't think it is too early to invest in Greece -- I just did it," he told CNBC.
With "outside help" Greece, Spain and Ireland have "done a very good job" of estimating worst-case losses, he said.
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"We are not as knowledgeable Italy as we are about the other two, but the general sense of things is maybe it is a little bit of an earlier stage of turnaround in Italy then it might be in Greece or Spain," he said.
The billionaire is set to pocket about 480 million euros ($650 million) from the sale of his entire 26.5 percent stake of the part state-owned Bank of Ireland, tripling his original investment in the lender according to reports.
Shares in Bank of Ireland fell over 3 percent in afternoon trading following the news. Ross has resigned from his role as director following the sale. The Irish government still own 14 percent of the bank.