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"We felt we needed to do something powerful and memorable. Billy seemed like the perfect choice," Emmy producer Don Mischer said at the red-carpet rollout ceremony, according to USA Today.
Aside from being friends outside the business, Williams and Crystal starred together in the 1997 Ivan Reitman film Father's Day.
Crystal has yet to comment on Williams' death other than through Twitter, on which he only stated, "No words," when news of the comedian's death broke. He hasn't posted to social media since.
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Williams was found dead in his home on Aug. 11. The actor committed suicide. His wife, Susan Schneider, also confirmed last week that Williams was in the early stages of Parkinson's disease when he died. The diagnosis had not previously been made public.
There has been a lot of speculation in the past week about if and how Williams would be honored during the show.
Mischer commented on the rumors in a statement. "Plans for the In Memoriam segment are in discussion. While we are all still coming to terms with this week's tragic news, we are working to give Robin Williams the proper and meaningful remembrance he so well deserves."
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The Academy also noted that Grammy-nominated singer-songwriter Sara Bareilles will be the featured performer during the In Memoriam. Bareilles recently dedicated her song "Hercules" to Williams, though it's unclear which song she plans to sing at the award show.
Last year, Williams honored Jonathan Winters during the Emmy segment.
Seth Myers is set as the host for the 66th Emmy Awards, which will air on Monday, Aug. 25 at 8:00 p.m. EST/5:00 p.m. PST on NBC.