Former Senator Antonio Trillanes IV on Monday urged Senator Imee Marcos to conduct an inquiry into the backchannel negotiations he initiated with China in 2012 and the "gentleman's agreement" between former President Rodrigo Duterte and China.

Trillanes issued the challenge against Marcos, who chairs the Senate Committee on Foreign Relations, in a post on X (formerly Twitter), where he also attached a video clarifying his role in the 2012 Scarborough Shoal standoff between the Philippines and China.

"Kindly watch this explainer to get a bit of background before speaking to the media," Trillanes’ captions read, a seeming response to Marcos’ accusation that he was duped by China in 2012.

In the video embedded in his post, Trillanes explained that he was designated by then President Benigno “Noynoy” Aquino III to be the country’s “backchannel negotiator” to de-escalate the tension in Scarborough Shoal.

“Just to be clear, being a backchannel negotiator is a foreign policy tool of a country to resolve problems that cannot be resolved by the formal or front channel of the Department of Foreign Affairs. This is not illegal,” he said.

The former lawmaker further noted that contrary to the claims by the allies of former President Rodrigo Duterte he did not sell the country’s territories to China.

“Whatever the Duterte supporters are insinuating that I supposedly sold Scarborough, this is clearly fake news,” he said.

“First of all, a senator does not hold the title to Scarborough Shoal, so how could I sell it? If that were true, then there should have been a deed of sale or any document shown by Duterte because they have all the documents in Malacañang and DFA,” he added.

Trillanes emphasized that his role as the backchannel negotiator of the Aquino administration was his "biggest achievement," as the number of Chinese ships in the shoal was reduced from 80 to 100 to just three.

"This was accomplished without surrendering even an inch of our territory. Scarborough Shoal still belongs to us. In short, I accomplished my mission," he said.

"Looking back, I can proudly say that this was my biggest achievement in my career as a public servant. An invasion or armed conflict with a regional power was averted through those backchannel talks," he added.

‘Gentleman’s agreement’

Trillanes also urged Marcos to probe the so-called “gentleman’s agreement” between Duterte and China.

“Better yet, I am requesting you, as the Chairperson of the Senate Foreign Relations Committee, to conduct an inquiry to shed light on the matter, and also include Duterte's secret deal in Ayungin,” he said.

Last week, Duterte’s former mouthpiece Harry Roque revealed that the former chief executive entered into a “gentleman’s agreement” with China to maintain the status quo in the West Philippine Sea.

Roque said the agreement was that the Chinese Coast Guard would not stop the delivery of food and water to the country’s troops stationed at the BRP Sierra Madre as long as the supply was limited to such.

Marcos earlier defended the gentleman’s agreement between Duterte and China, stressing that “it was the practical thing to do.”

“It was exaggerated. Their reactions were OA [overreacting]. This is not the first time that a deal was made if ever there was,” she said in a radio interview, referring to retired Supreme Court Justice Antonio’s accusation that the former president “gave up” the country’s sovereign rights over Ayungin Shoal when he made such an agreement with China.

“For me, the agreement to allow the Philippines to send food and other necessities to Filipinos there [BRP Sierra Madre] was practical,” she added.

She asserted that she did not see anything wrong with the said agreement.

“For me, the agreement of PRRD was okay. There was no treason. There was no giving up on sovereign rights. They just agreed to allow the delivery of supplies peacefully,” she said.

“We need to talk to them. When you put the lives of soldiers or officials in danger, you are an irresponsible official. Let us not put the lives of Filipinos in danger,” she added.