[(If the) truth BE told] is an idiomatic construction in English with a number of pragmatic purposes. It can suggest that a proposition is generally known but rarely admitted, or that a proposition is a previously unknown personal admission. It can also act as a pragmatically weaker discourse marker. This study initially looks for early uses in the Early English Books Online (EEBO) corpus, finding examples from the late 16th and early 17th centuries. Diachronic changes in the use and form of the construction in American English are then examined using the Corpus of Historical American (Davies 2010), which contains texts written between 1810 and 2020. In COHA the [(if the) truth BE told] construction becomes considerably more frequent after 1980. Coinciding with this increase in frequency the construction becomes more lexically fixed and reduced in length. It also becomes more likely to appear at the left periphery of a clause. In addition, it appears to be moving towards ‘extended intersubjectivity’ (Tantucci 2017). As such, it is increasingly losing its pragmatic purposes of marking a rarely admitted truth or a personal admission, and behaving more like a simple discourse marker, connecting clauses.