The ex-US diplomat who spearheaded Washington’s efforts on North Korea said officials in Pyongyang were “surprised” that President Trump was so quick to agree to a sit-down with leader Kim Jong Un.

“To be frank with you, I think they were a little bit surprised that Washington, President Trump readily accepted,” Ambassador Joseph Yun told CNN. “They thought it would take a little time.”

Yun, who stepped down as US special representative for North Korea policy, said he welcomed the planned May meeting between Trump and Kim.

“I’m very supportive of (Trump’s) decision to engage at the highest levels,” Yun said. “That is a great outcome.”

To the surprise even of his advisers, Trump readily accepted an invitation to meet Kim in hopes of securing the rogue regime’s complete denuclearization.

“I think North Korea is going to go very well,” he said last week. “I think we will have tremendous success … they promised they wouldn’t be shooting off missiles in the meantime, and they’re looking to de-nuke. They’re gonna be great.”

The decision follows talks between North and South Korean officials during the 2018 Winter Olympic Games in PyeongChang.

“They now have nuclear weapons and a delivery system that can legitimately threaten all states in the United States,” Yun told CNN on Thursday about the North.

“That is different from the past, where we were trying to stop them from getting there, so it requires different attention, different focus and a different approach.”

Yun served as the State Department’s point man on North Korea for 16 months, first under then-President Obama and then under Trump.

In that role, he held back-channel talks with North Korean officials, and traveled to Pyongyang last year to help secure the release of imprisoned US student Otto Warmbier, who died shortly after his return to the US.