There is an expression in Malayalam -an Indian language- which translates into English as "a black ant in the heaven". It roughly means an intruder into one's privacy. It is particularly used to refer to a person who knowingly or unknowingly disturbs the privacy of couples/lovers by joining them when they wanted to be alone. This black ant may be one of their friends, but is unwelcome now in their private moments.
Is there a word or an idiomatic phrase to refer to such a 'black ant'? Or, is it understandable to the native ears the term "a black ant in/of the heaven"?