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By Dakshayani Shankar

David Letterman is making a rare return to the small screen — and it's no laughing matter.

The former "Late Show" host will serve as a correspondent for an episode of the National Geographic Channel's docuseries, "Years of Living Dangerously," for its second season Oct. 30.

The 69-year-old comedian traveled to India and met Prime Minister Narendra Modi to explore how one of the world's largest populations is making the move from non-renewable energy to solar power.

"My goal here is a conversation — containing several points both personal and with regard to environmental issues and climate change," Letterman said in a recently released behind-the-scenes video, teasing his preparation for his interview with Modi.

The Emmy Award-winning series features Hollywood celebrities investigating various climate change issues and discovering new ways to reduce it. The producers of the show, David Gelber and Joel Bach, said they chose Letterman because they could see his enthusiasm for clean energy and felt he was "invested in the issue."

"I've created, excuse the expression, kind of a love affair with this," Letterman in a promo teaser said of his passion for climate change, particularly clean energy. "Think about the coal-fired, dangerous, smoke-belching generating plants, and then you look at this and it's friendly. There's something very appealing about this, and it's smooth. Look at this. I can touch it and it's safe."

Letterman — now sporting a fluffy beard — retired as a late-night talk show host in May 2015 and has stayed away from television projects since.