GREP Code for Photo Credit Line

I am laying out a large book that contains photos, and therefore, photo captions. The caption copy will vary in length throughout the book depending on the photo; but, in every case the last line of text in the caption will be a photo credit line (“Photo by [photographer’s name].”). This line will be a part of the same paragraph—not in parentheses, and not separated by anything but a period.

My goal is to set up this singular photo credit line to auto-format in a different character style. It seems that the “Next Style” feature and Nested Styles are out since the photo credit line is part of the same paragraph and not separated by a forced line break or hard return. So, I’m thinking perhaps I need to set up a GREP Style. I’m so very new to GREP styles that I haven’t the faintest idea how to create the proper code that will accomplish what I’m trying to do. Can someone please help me generate one?

Thank you!