MANILA - President Rodrigo Duterte on Monday revealed the real reason behind his absence in last week's Association of Southeast Asian Nations (ASEAN)-United States (U.S.) Summit in Laos.

In a speech in Malacañang, Duterte said he skipped the regional group's meeting with U.S. President Barack Obama as a "matter of principle."

"I did attend, but I purposely did not attend the bilateral talks between ASEAN countries and the ambassador of, the President of the United States. Talagang ini-skip ko 'yun. I attended all others. 'Yung kay (Russian President Vladimir) Putin (sic), may one-on-one ako, and the ASEAN and also the Chinese, I was there. The reason is not I am anti-West. The reason is not I do not like the Americans. It's simply a matter of principle for me," Duterte said.

(Editor's note: Russia was represented by at the ASEAN Summit Russian Prime Minister Dmitry Medvedev.)

Last Thursday, Presidential Adviser on the Peace Process Jesus Dureza said Duterte had to skip the ASEAN-US and ASEAN-India summits in Vientiane because the chief executive ''was not feeling."

Secretary Dureza on why President Duterte skipped two meetings today: pic.twitter.com/V3c6YbiZ8Z

— Willard Cheng (@willardcheng) September 8, 2016

Foreign Affairs Secretary Perfecto Yasay represented Duterte at the ASEAN-US Summit last Thursday.

President Duterte unable to attend ASEAN Summits with US President Obama and India PM Modi pic.twitter.com/RFjGb0iF6Q

— Willard Cheng (@willardcheng) September 8, 2016

Duterte was also unable to attend the ASEAN-United Nations Summit last Wednesday. Yasay also attended the event for the president.

WATCH: Pres. Duterte bares truth on not attending the ASEAN-US meetings at the ASEAN Summit | via @dzmmRP45 pic.twitter.com/N638F7ltek

— ABS-CBN News (@ABSCBNNews) September 12, 2016

The ASEAN-US Summit meeting would have been another chance for Duterte to meet US President Barack Obama after the White House cancelled the bilateral meeting between the two leaders following Duterte's tirade against the US before leaving for Laos.

However, Duterte and Obama already had a brief meeting on Wednesday evening at the ASEAN gala dinner.

READ: Obama: I didn't take Duterte's cursing personally