Under the relevant regulations, a "first-time borrower" is "a borrower to whom no housing loan has ever before been advanced". If you drill down into the definitions, a "housing loan" is advanced by a "lender"; a "lender" is defined as a "regulated financial services provider", and "regulated financial services provider" is a financial services provider whose business is regulated by the Central Bank of Ireland or by a similar authority in another EEA country.
The UK isn't an EEA country, but it was until 2019. So, assuming that the house that ChampionCharlie used to own in the UK was financed with a loan from a UK-regulated lender, ChampionCharlie is not a first-time borrower.
But.
The regulations concerned are not directed at borrowers, and don't say how much borrowers can borrrow. It's aimed at lenders, and it says how much lenders can lend. All the obligations under the regulations are imposed on lenders.
Which means that, if an Irish lender advances 4xsalary to CC, CC does nothing wrong, improper, unlawful, etc and they haven't breached any regulations (assuming they answered the lender's questions fully and truthfully, of course). The lender may be at fault for not having asked CC the right questions, and so lending 4xsalary to someone who, they should have found out, is not a first-time borrower.
In other words, if a lender advances 4xsalary to CC, that's not CC's problem; it's the lender's problem.