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Matt Lauer creepily whispered to Meredith Vieira ... "Keep bending over like that. It's a nice view" -- and it happened on set, while cameras were rolling.

This all went down in October 2006, and it's a little bizarre how it got out to the public. The show had gone to commercial, but in at least one city, the local affiliate stayed on NBC's in-studio feed. Matt was seen sitting on the couch as Meredith got mic'd up.

As she leaned over in front of him to grab scripts, you clearly hear Lauer say, "Pretty sweater. Keep bending over like that. It's a nice view." The video never shows a clear view of Meredith's face -- and we initially thought it was Katie Couric -- however the timing makes sense. Meredith took over for Katie in Sept. 2006.