On Thursday, Donald Trump took to Twitter to call for increased U.S. nuclear capability until “the world comes to its senses regarding nukes.”

Japanese-American actor George Takei had a powerful response for the president-elect that called to mind the past horrors of nuclear weapons.

Trump wants to expand our nuclear arsenal. I think of my aunt and baby cousin, found burnt in a ditch in Hiroshima. These weapons must go. — George Takei (@GeorgeTakei) December 22, 2016

Takei has a highly personal reason to take issue with Trump’s tweet. Members of his family were living in Hiroshima during WWII, when the U.S. dropped a nuclear bomb on the city on Aug. 6, 1945, killing thousands instantly and some 140,000 by the end of the year.

Takei’s aunt and cousin were among those who lost their lives, “found burnt in a ditch in Hiroshima,” the actor wrote. “These weapons must go.”

Earlier this year, Barack Obama became the first U.S. president to visit Hiroshima, where he mourned the lives lost and called for an end to nuclear weapons.

JIM WATSON via Getty Images U.S. President Barack Obama hugs a survivor of the 1945 atomic bombing of Hiroshima, during a visit to the Hiroshima Peace Memorial Park on May 27.

“Amongst those nations like my own that own nuclear stockpiles, we must have the courage to escape the logic of fear and pursue a world without them,” Obama said in a speech.

In an opinion piece for The Guardian, published in May, Takei praised Obama’s visit to Hiroshima.

“I share Obama’s call for a nuclear-free world,” he wrote. “We must pledge to work closely with other powers, to reduce not only the number of weapons in our arsenals, but also the numbers of states bearing or seeking to bear them.”