Why, what did he say?
"I'm going to tell you about the Nobel Peace Prize, I'll tell you about that. I made a deal, I saved a country, and I just heard that the head of that country is now getting the Nobel Peace Prize for saving the country. I said: 'What, did I have something to do with it?' Yeah, but you know, that's the way it is. As long as we know, that's all that matters... I saved a big war, I've saved a couple of them."
Who was he talking about?
Although he did not name the Nobel Peace Prize winner or the country, it is clear that Mr Trump was referring to Ethiopian Prime Minister Abiy Ahmed.
Mr Abiy, 43, is Africa's youngest head of government.
He came into office in April 2018 after months of anti-government protests forced his predecessor to resign.
Mr Abiy has introduced massive liberalising reforms to Ethiopia, shaking up what was a tightly controlled nation.
He freed thousands of opposition activists from jail and allowed exiled dissidents to return home. He has also allowed the media to operate freely and appointed women to prominent positions.
And in October last year, he was awarded the Nobel Peace Prize - the only head of state to win the prize since Mr Trump was elected in 2016.
Why did he win the Nobel Peace Prize?
The Norwegian Nobel Committee said Mr Abiy was honoured for his "decisive initiative to resolve the border conflict with neighbouring Eritrea".
The two countries fought a bitter border war from 1998-2000, which killed tens of thousands of people. Although a ceasefire was signed in 2000, the neighbours technically remained at war until July 2018, when Mr Abiy and Eritrea's President Isaias Afwerki signed a peace deal. So for two decades, the long border was closed, dividing families and making trade impossible.
The Nobel Committee said it hoped the peace agreement would help to bring about positive change to the citizens of Ethiopia and Eritrea.
Since the peace deal with Eritrea, Mr Abiy has also been involved in peace processes in other African countries, the committee said.