WASHINGTON — Almost six years ago, in September 2011, Jon Underwood held his very first ‘‘death cafe’’ in the basement of his home in east London. He put out tea and cake and had people gather to talk about death, mortality, and the finitude of life.

That first cafe, inspired by the ideas of Swiss sociologist Bernard Crettaz, who developed the concept of ‘‘cafe mortels,’’ has since spawned a worldwide movement.

Thousands of death cafes have been held in more than 50 countries, including the United States.

Other than to talk about death, the cafes had no agenda. Anyone could join, whether or not they were religious, superstitious, or spiritual.

Then, on June 27, Mr. Underwood died from undiagnosed leukemia. He was 44.

The unexpected abruptness of his death came as a shock, especially to his closest family. But Mr. Underwood’s philosophy of life and death is also a strange source of comfort at this devastating time, said his sister Jools Barsky.

‘‘There is a bizarre irony about dealing with the sudden death of my brother, who devoted his life to raising our awareness about the fact [that] life is short and unpredictable,’’ Barsky wrote in an e-mail. ‘‘Whilst in some ways the irony is unimaginably horrible, in others it is strangely helpful.’’

‘‘Jon was uniquely and unusually aware that life is short, and appreciated his life fully, reflecting on this through daily practice,’’ wrote Donna Molloy, his widow, in a blog post.

Mr. Underwood, who was constantly searching for spiritual meaning, was keen to instill his philosophy of life and death in his family.

‘‘He would often say ‘‘well Jools, you never know, you could be dead tomorrow!’’ Barsky told the Post.

She added that Mr. Underwood ‘‘pushed me very hard, sometimes what felt like too hard, to really take advantage of every opportunity and experience.’’

The death of Mr. Underwood will not spell the end of Death Cafe.

As per Mr. Underwood’s request, his sister and his mother, Sue Barsky Reid, will continue his work on the Death Cafe movement. Barsky emphasized that however the movement proceeds, it must be ‘‘very carefully considered and approached in a thoughtful way. This must be a way that Jon would have approved of, and that holds true to the core principles of Death Cafe of allowing people to talk about death in a safe space,’’ wrote Barsky.