Last instance of a character

How do I identify the location of the LAST instance of particular character (base zero)?

C:\\Location\Folder\Folder\Files.xlsx|Sheet1  has its last "\" at character 26

C:\\Location\File.txt   has its last "o" at character 10

C:\\Location\Folder\Folder\Folder\Folder\FileswithSheets.xlsx|Sheet1  has its last "|" at character 61

I assume I need some regex, but I'm not very confident using regex yet.