"He is absolutely distraught," Butler says.
Butler says the woman was in her 50s and from the village of Robinstown, County Meath, northwest of Dublin.
The Irish Department of Foreign Affairs says it cannot confirm whether an Irish citizen is among those killed in Friday's attack. It says more than 60 Irish holidaymakers are in the country.
Another group of Irish holidaymakers due to depart Friday night to Tunisia have had their bookings refunded.
And Spain has raised its terror threat level to the second highest level on its scale as a precautionary measure following the suspected terror attacks in Tunisia, France and Kuwait.
Interior Minister Jorge Fernandez Diaz told reporters the level was raised from 3 to 4, meaning the country faces a high risk of a possible attack. Spain's highest terror threat level is 5.
Spanish officials have no information suggesting that the country faces an imminent attack, Fernandez Diaz said.
A gunman killed at least 28 people and wounded 36 in an attack on a beach resort in Tunisia Friday. In Kuwait, a suicide bomber killed at least 25 people, while a man with suspected ties to French Islamic radicals rammed a car into a gas factory in southeastern France, triggering an explosion that injured two people. The severed head of a local businessman was left hanging at the factory's entrance.