I became a Florida resident in 2018. Do I have to include income from a pension from the government of Puerto Rico and for which I already paid taxes to PR?

I have a fellow retiree from Puerto Rico who claims his accountant told him not to include that income in the Federal Return and file and pay taxes in Puerto Rico only.  He even got a letter from the IRS stating he did not have to include it.  

Just want to make sure and avoid any kind of penalties.