The accepted answer shows all the commits in all branches, which is not exactly what was set, and often shows too much information to understand. You can do the following to view only one remote branch.
Run git fetch as usual, either from TortoiseGit or from the command line.
In the Log Messages dialog box, click on the blue branch name in the upper left corner to open the Link Overview dialog box 
In the "Browse Links" dialog box, select the remote branch that you want to view, most likely it will be in the section refs-> remotes-> origin. Then click OK to return to the Log Messages dialog box. The commit history should now display information about the selected remote branch.

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