President Trump said in an interview with Fox News that he personally doubts UFOs exist, but added he couldn’t definitively say unidentified aircrafts are only the stuff of science fiction.

Trump made the statement to Tucker Carlson in a pre-recorded interview, part of which was aired on Friday.

“Well, I don’t want to really get into it too much. But personally, I tend to doubt it,” Trump said in the interview, which was recorded during his trip to Korea last week. “I’m not a believer, but you know, I guess anything is possible.”

Carlson asked Trump about UFOs as the fringe theory about visitors from foreign planets has been getting plenty of attention in recent weeks. In June, three senators, including Intelligence Committee Vice Chairman Mark Warner, were briefed by the Pentagon about recent reports of UFO sightings by Navy pilots.

In his remarks to Carlson, Trump referenced the reports by the pilots.

“I mean, you have people that swear by it, right?” Trump said.

“And pilots have come in and they said — and these are pilots that have — not pilots that are into that particular world, but we have had people saying that they’ve seen things,” he added.