The fourth diddle rudiment diddle or double that you'll find in a list of those rudiments, is called a single paradiddle diddle. Or, what we just call paradiddle diddle.
Now, what it is, is exactly what it's saying. Para diddle diddle, meaning a set of singles, para, followed by a diddle which is a double on one side, and then a double on the other side. Now, this one does not alternate. If you're starting with your strong hand, you're going to start with that hand, it's going to end on your weak hand and then you're going to restart it on your strong hand again.
Once you've practiced it on one side, my suggestion is to repeat it on the other side, to build that side up as well. I'm going to play it on the right side so you can hear it slowly, and then work it up in time, faster.
The paradiddle diddle is a very interesting rudiment to play around the drums, as you can take that accent and displace it to different surface, and also add little grace notes on the base drum or the high hat, or some areas into it. So, a mix of paradiddle diddles on a different surface would sound something like this.
The paradiddle diddle is very interesting, that it could be more of a drum fill or a drum solo rather than just a drum rudiment itself. Either way, make sure to get the rudiment right. Make it clean, and practice it on both sides of your body.