Gerry and Kate McCann revealed that half the letters of support they received had come from this country.
And hundreds were sent from Donegal – where Gerry has many relatives.
Last night on the Late Late Show on RTE1, Mr McCann spoke briefly about his Donegal connections.
He said his two brothers and sister were born in Donegal but that he was born in Glasgow.
“It was a big happy Irish Catholic family,” he told Ryan Tubridy.
In an emotional and heart-breaking interview Kate McCann retold the horror of discovering her daughter missing from their holiday apartment in Portugal in May 2007 – a few days short of her fourth birthday.
All royalties from the book will help fund the search for Madeleine, a search boosted this week when British PM asked the London police to review all evidence in the case.
Gerry’s family are from St Johnston but he has relatives throughout the county and in Glasgow.