MANILA- Foreign Affairs Secretary Alan Peter Cayetano will leave President Rodrigo Duterte's Cabinet to run in the 2019 polls.

Duterte said he already has a replacement for the plum post.

"I have a name, he agreed. But he did not authorize me to name him now," said Duterte before the Malacanang Press Corps on Tuesday.

ABS-CBN News sources however said Permanent Representative to the United Nations Teddy Boy Locsin may be tapped to replace Cayetano.

Prior to Duterte's announcement, sources earlier told ABS-CBN News that Cayetano already sought Duterte's permission to run as congressman of Taguig in the 2019 polls.

One of the sources, however, said Cayetano will remain in office until November this year for the scheduled visit of Chinese President Xi Jinping.

The Philippines and China are hoping to sign an agreement on joint exploration for resources in the South China Sea.

Filing of certificate of candidacy for the May 13, 2019 mid-term elections is from October 11 to 17, 2018.

But based on the 2019 election calendar drawn up by the Commission on Elections (COMELEC), substitution of candidates due to withdrawal is allowed until November 29, 2018.

The Comelec has also relaxed substitution rules to allow substitution of candidate until mid-day of election day: provided that the substitute bears the same surname as the one being substituted, and the substitution is due to death or permanent incapacity.

The congressional seat for the 2nd district of Taguig is currently occupied by Secretary Cayetano's older sister, Rep. Pia Cayetano.

Pia, however, has indicated she will be making a Senate comeback.

In 2016, Secretary Cayetano ran for vice president while in the middle of his second Senate term.

After the one year ban on losing candidates, he was appointed to the Department of Foreign Affairs.

Sources said Secretary Cayetano was aiming to become House Speaker in the 18th Congress.

ABS-CBN News reached out to Secretary Cayetano for confirmation, but he has yet to respond as of posting.