He told reporters on Air Force One that he had delivered his prepared remarks during the lunch instead of the summit meeting.
"It is the first prime ministerial visit in thirty-six years from India to Philippines".
In another unusual and candid moment from the ASEAN summit, Duterte - who recently said he stabbed someone to death when he was a teenage because of "a look" - sang a Filipino love song "on the orders of Donald Trump" shortly before the summit.
ATP Finals: Grigor Dimitrov edges Dominic Thiem on his London debut
It was Thiem, who made his debut at the event previous year , who started nervously, allowing Dimitrov to ease to the opening set. I was like, Not again, definitely not again. "I think the best is yet to come".
More than 3,900 pushers and users have been killed in the war on drugs that Duterte declared when he took office a year ago. Secretary of State Rex Tillerson would attend the plenary session in his place, a senior White House official said. His government says the police act in self-defense, but critics say executions are taking place with no accountability.
In a meeting Monday, Trump praised Duterte's hospitality and said nothing about human rights, including the thousands killed in the country's blood drug crackdown.
"I just wanted to congratulate you because I am hearing of the unbelievable job on the drug problem", Trump said in the April 29 phone call.
On the ground, military operations continue to clear buildings for stragglers.
Trump and Duterte were joined by more than a dozen other leaders from Southeast Asia, Australia, Canada, Russia and India.