MANILA — Former lawmaker Antonio Trillanes IV, a staunch critic of President Rodrigo Duterte, filed on Friday his certificate of candidacy (COC) for a return to the Senate in the May 9, 2022 elections.

The former senator earlier said he would run for President if Vice President Leni Robredo did not seek the highest post. On Thursday, he announced he would run for senator under Robredo's slate.

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Trillanes and Robredo battled it out in the 2016 elections but have since become allies against the drug war and China policy of President Rodrigo Duterte.

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The 50-year-old Trillanes has sparred numerous times with Duterte, accusing the President of hiding ill-gotten wealth and backing several complaints to the International Criminal Court (ICC) seeking the President's indictment for crimes against humanity.

Duterte denies wrongdoing and has repeatedly said he would resign if the allegations were proven.

In 2018, he scrapped the amnesty for Trillanes' involvement in a failed 2003 coup and a mutiny 4 years later, both aimed at overthrowing then-President Gloria Macapagal Arroyo, a Duterte ally.

Trillanes graduated cum laude from the Philippine Military Academy and was a Navy officer.

— With a report from Reuters