A clean, closed form, joint density is derived for Brownian
motion, its least concave majorant, and its derivative, all at the same fixed
point. Some remarkable conditional and marginal distributions follow from this
joint density. For example, it is shown that the height of the least concave
majorant of Brownian motion at a fixed time point has the same distribution as
the distance from the Brownian motion path to its least concave majorant at the
same fixed time point. Also, it is shown that conditional on the height of the
least concave majorant of Brownian motion at a fixed time point, the left-hand
slope of the least concave majorant of Brownian motion at the same fixed time
point is uniformly distributed.