President Trump and Spanish Prime Minister Mariano Rajoy met at the White House on Tuesday, and afterward they said in a joint news conference that they had discussed fighting terrorism, North Korea, and other threats to democracy. Nevertheless, it was presumably a nice meeting. Trump thanked Rajoy in a tweet Tuesday evening, referring to him as "President MarianoraJoy."
Spain is a constitutional monarchy, and while the prime minister's Spanish title, presidente del gobierno, translates directly as "president of the government," the Spanish leader is formally referred to in English as prime minister. Presumably, Trump knows all that. Rajoy, a conservative, has been prime minister since 2011.