Keith Byrne's father Jim told RTÉ radio's Morning Ireland that his son was still in shock over his release from detention in the US when he spoke to him by mobile phone on Thursday evening.
A US federal judge on Wednesday ordered the release of the 37-year-old Cork man and has since been reunited with his family.
"I was talking to him in the car as he left the facility. My mind was blown. You don't know the relief," Jim Byrne said.
Keith Byrne was arrested by ICE last week, having overstayed his Esta visa waiver when he entered the country in 2007. His green card applications were refused due to previous minor offences for marijuana possession.
Mr Byrne will be temporarily released for a period of 30 days to allow him to seek judicial review of the decision to deny him legal status in the US.
However, the order states that "nothing . . . precludes the United States and ICE from redetaining Keith Byrne or reinstituting removal proceedings".
He is married to an American woman and they have three children, including his wife Keren’s son from a previous relationship.
Jim Byrne had been in hospital when his son was first detained by the US Immigration and Customs Enforcement (ICE).
‘Long fortnight’
“It’s been a long fortnight and to see his name on the phone was brilliant,” Mr Byrne said.
He is now much more optimistic about this son’s chances of remaining in the US. “I’ve been reading a lot about such cases – there were 45 Irish people deported last year. It seems that what you cannot do is come in contact with the law.
“He’s been there 12 years and he’s never had any brush with the law.”
His son anticipates “a lot of attention” in the morning and does not know how he’s going to “handle it”.
He’s now looking forward to spending the weekend with his wife and family.
Melinda Byrne (sister of Keith), added that her brother will be seeking an extension to the 30 days he has been given to prepare his case which will be heard before a federal judge.
"He will be taking it day-by-day. It is great that he can make his case in the local area in Philadelphia. That relieves the pressure."