I'll bite... the 'brief partial nudity'... might it be Biel?

SPOILER
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Sorry to disappoint, but I believe they are referring to the scene where Kimberly Nixon "moons" the crowd at the end of a performance of the can-can.

However, in the sensuous tango scene with Colin Firth at the end of the movie, Jessica Biel is wearing a slinky satin gown that leaves little to the imagination, and director Stephan Elliot reveals during the commentary that he asked her to do the scene without undergarments.

That was tacky of Kimberly to embarrass her SIL and family like that. I didn't know about Biel sans undergarments in the tango scene. That is kinda gross the director would tell her to do that.

There is also the scene in the folly. Brief, but very funny.