MANILA -- The son of presidential bet, Davao City Mayor Rodrigo Duterte has issued a request to his father's rival, Miriam Defensor-Santiago, ahead of the final presidential debate Sunday.

"I wish you all the best. P.S. Bring the best out of Mayor Rodrigo Duterte, give him the fight of a lifetime!" Sebastian said in a Facebook post Sunday.

Sebastian also wished Santiago luck, as he recalled the time he saw the senator in person.

"I feel so lucky that I had the chance to have a picture with you. To my surprise, you even went over to me when my friend asked for a photo. I was so captivated by your presence that I did not know what to do," Sebastian said.

Santiago's camp said the meet-and-greet took place at the Davao City airport before the senator left for Manila last week.

Sebastian described Santiago as "sweet and inspiring," and lauded her contributions.

"I never easily get starstrucked (sic) but you had me at mere sight. I truly admire you because I believe that you are a real contributor to our country," Sebastian added.

(READ: Duterte boosts lead in new ABS-CBN survey)

Santiago and Duterte will go head-to-head in the final presidential debate Sunday, along with three other candidates, Jejomar Binay, Manuel Roxas, and Grace Poe.

Candidates will bare platforms and stand on issues before a live audience, in a program aired on ABS-CBN Channel 2, simulcast on cable channel ANC and radio dzMM. Livestreaming is also available on NEWS.ABS-CBN.COM and iWantTv. The debate is in partnership with Manila Bulletin and KBP.