Sorry, no audio, so I'll have to type out the steps.
First, I chose the Lasso tool with a Feathered Edge radius set to 100. I selected as much of the right side of the image as possible. I then applied a Gaussian Blur to the selected right side of the image. I then repeated the same process, each time applying a Gaussian Blur with a higher radius (5 to start, ended with 30). When using the Lasso tool, I'm able to 'select' the white canvas outside the image, so all you see in the screen capture is a line ("marching ants") on the image itself. Everything to the right of the line is selected to apply the Blur.
As you can see in the video, I start to select less and less of the image until I choose the top left and the bottom right.
So each step was applied to a smaller area, but a higher blur radius, as I selected smaller areas.