This is entirely due to Brexit, there is no free trade between the UK and Europe (including the Republic of Ireland) and customers are subject to charges. We DID tell the customer this. Our email to him included this (and it was typed in red and highlighted in yellow):
"We do not charge VAT (sales tax) on sales to the EU. When the parcel arrives in your country you must pay the VAT plus a service fee. In some countries the process is simple, you are notified by email, you pay online, it takes five minutes; in other countries the item is held at customs for several days while you arrange customs clearance"