I want to get the natural width of the last line in a paragraph. For example, the last line of the following paragraph
Georg Friedrich Bernhard Riemann (September 17, 1826 – July 20, 1866) was an influential German mathematician who made lasting contributions to analysis, number theory, and differential geometry, some of them enabling the later development of general relativity.
may be from
some of them enabling the later development of general relativity.) When the line-breaking happened, the last line will be put into an hbox, so, how can I get this hbox?