As an American he must file American taxes every year. There are penalties for not doing that. I am very shocked he did not know that. There is a fee to renounce US citizenship. $2350 last I know plus an exit tax on ALL your assets. Boris Johnson had to do this. It cost him big time. He was born in NYC.

I know this because I was born in the USA and came to Canada in 69. I found found out I had to file taxes every year. I made too little to have to pay anything to the USA. I kept filing my US taxes up to the year I became a Canadian. When FATCA surfaced and was a very talked about law I decided to give up my US citizenship. I did it with a lot of paperwork. I didn't renounce, I relinquished. There are so many variables. some people could only renounce and pay the exit fee and tax on their assets. Some had very heavy penalties.

Hard to believe he did not know this. it was in the news alot.

Most duals I know did not. They were unaware they had to