Of course, she's famous for her Sports Illustrated swimsuit shoots, but instead ... Kate slipped into lingerie for a shoot this weekend with Yamamay. She posted a bunch of behind the scenes shots -- God bless her -- from her day at the office.

Kate rocked several different pieces -- white, black, blue -- and captioned her pics, "#confidentbeauty."

Ummm, we didn't realize there was any other kind of beauty for Kate Upton ... but okay.