In a clip from Monday night's Conan, O'Brien addressed the crowd about Williams' death, and said although the show would not air for a few hours, he wanted to let people know the sad news.
"This is unusual and upsetting," O'Brien said. "But we got some news during the show that Robin Williams has passed away."
Following the audible reaction of the audience, the late-night host apologized for breaking the story, but said he felt it was needed to acknowledge the situation before the taping ended.
"This is absolutely shocking and horrifying and so upsetting on every level," O'Brien continued. "Obviously we don't know much yet, but we know that this has happened and we are absolutely stunned."
O'Brien then addressed his two guests, show writer Andy Richter and actor Will Arnett, revealing how they've all worked with Williams over the years, and gave the pair time to give their own tributes to the late comedian.
"He was an amazingly kind and generous person. It's got to be a terrible time for his family, and our thoughts go out to them," Richter said.
"As funny as he was, he was truly one of the all-time greats," Arnett said. "He was even better in person, he was even more fantastic... he was just one of the loveliest, sweetest, kindest guys that I've ever worked with, such a soft, warm, emotionally sweet guy. It's a major, major loss for everybody."
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