This verse is not part of the psalm; it is the concluding doxology of Book Three (Psa 73–89); see similar concluding doxologies in 41.13; 72.18-19.
Quoted with permission from Bratcher, Robert G. and Reyburn, William D. A Handbook on the Book of Psalms. (UBS Helps for Translators). New York: UBS, 1991. For this and other handbooks for translators see here .