Skeleton(s) in the closet/cupboard

To have a secret of any sort that you don't want revealed, a hidden and shocking secret.- un cadavre dans le placard

• My uncle was in jail for a day once. That's our family's skeleton in the closet.

Origin:

The phrase 'a skeleton in the closet' was coined in England in the 19th century. Since then the word 'closet' has become used primarily in England to mean 'water closet'. The English now usually use 'a skeleton in the cupboard', with 'skeleton in the closet' more common in the USA.

'A skeleton in the closet' undoubtedly originated as an allusion to an apparently irreproachable person or family having a guilty secret waiting to be uncovered. The close-at-hand domestic imagery of a closet or cupboard gives a sense of the ever-present risk of discovery.