It is so hard to find diaper bags that fit double strollers! The struggle is real. This fits perfectly on my side by side double stroller (City Mini GT) as well as other strollers. It has these neat clips on the ends to help keep it attached. This diaper bag offers A LOT of storage and is in great condition.
It appears that they no longer make the black version, but you can see the specs of the gray online. (Amazon)