The volleyball star will lead the all-Filipina parade of Team Philippines during the opening rites at the Morodok Techo Stadium in Phnom Penh.
Valdez will leave for Phnom Penh on Friday, a day ahead of the entire women's volleyball team, in order to make it to the opening ceremony after getting the nod from the Philippine Olympic Committee.
It will be the second time she will carry the flag, having done so in 2015 in Singapore.
"It’s such an honor to be the flag bearer for this year’s SEA Games," said Valdez. "It’s a big responsibility but I’m grateful for the trust given to me once again."
"I first had the opportunity to carry our Philippine flag in 2015 in Singapore and it was an unforgettable experience.”
Fifty Filipina athletes will represent the country in the parade of nations.
"Alyssa best fits our goal of an almost all-female delegation in the opening ceremony,” said POC president Abraham 'Bambol' Tolentino on Tuesday. “She’s not only the face of Philippine volleyball, but Philippine sports as well.”