a ghost at the feast
a ghost (or spectre) at the feastsomeone or something that brings gloom or sadness to an otherwise pleasant or celebratory occasion.
The ghost or spectre of Banquo at the feast in Shakespeare's Macbeth is the most famous literary instance of this. There are other versions of the expression. A skeleton at the feast dates from the mid 19th century and probably refers to the ancient Egyptian practice of having the coffin of a dead person, adorned with a painted portrait of the deceased, present at a funeral banquet. A death's head at the feast alludes to the use of a death's head or skull as a memento mori (an object which serves as a reminder of death).