Trillanes made his apology and explained his untoward actions through a letter sent to Cayetano's office on Monday, GMA News reported.
"This is to express my apologies for my demeanor during last Thursday's hearing of the Committee on Justice and Human Rights. It was brought about because of the intense passion and emotion of the moment. Nonetheless, it was uncalled for," the letter read.
"Be assured that such incident will not happen again," it added.
Trillanes’ apology comes days after he said he did not regret his actions against Cayetano.
Trillanes initially argued that Cayetano was taking up too much time in questioning the witness but he shot back saying he had the right to do so as a senator which almost led to a fistfight.