Thomas Markle's Son Who Reported Him Named Person of Interest in Child Porn Probe

Thomas Markle Sr.'s son Thomas Jr. has been named a person of interest in the investigation into his father's alleged child porn possession ... Philippine officials revealed.

In a press conference Thursday ... Philippine Interior Secretary Jonvic Remulla said ... "We have a witness [who says] underage girls were being brought to his house. We will investigate whether the son was involved in the crime."

Remulla added ... "To accuse the father only is only half the police work. There are signs that point that the son is involved in the crime as well but only as a person of interest so far."

While Thomas Jr. -- who reported his father to Philippine officials -- is under investigation ... he is currently not a suspect. News5 Philippines broke the story.

We've reached out to a rep for Thomas Jr. for comment ... so far, no word back.

Thomas Jr. being named a person of interest comes after he told The Sun that he reported storage units Thomas Sr. rented in Hollywood to the FBI.

He told the outlet ... "There's something there, that's my gut feeling, I dread to think what the FBI might find, especially given what has been found in the Philippines and Mexico."

As you know ... authorities in Mexico and the Philippines are investigating Thomas Sr. for alleged child porn stashes.

In their search, Mexico officials had allegedly found child sex abuse images ... while Remulla previously said their discovery included material that pointed to a sex offender of "the grossest kind."