In total, more than 20 works are being offered at Christie's by Neil and Monte Wallace, brothers who are now both in their 80s. The brothers founded real estate and investment company General Investment & Development Cos. (GID) about 60 years ago. Now, the firm develops and operates more than $15 billion in real estate assets.

Some of the rare works being offered as part of the "Hidden Treasures: Impressionist & Modern Masterpieces from an Important Private Collection" sale, have not made public appearances in over three decades, but for the occasional museum appearance. The collection was called "intensely private" and the "most important single owner group of Impressionist and modern art offered in London in a decade" when it was unveiled in Hong Kong.