QGIS - Atlas Settings - Dynamic Text Base on Grid Attributes

Question

I have multiple grids in my project file. I am utilizing Atlas to automatically print all grids. I was successful yet I have added "SEE SHEETS A1..." within the sides of the mapview as required by our client. What I think now to solve this is similar to Dynamic Text. Yet I wasn't able to figure it out.

The output is should be like this:

Answer 1

This can be done with the aggregate function in expressions:

for example the northern neighbour:

aggregate(layer:='your_grid_layer',
          aggregate:='concatenate',
          expression:='See sheet ' || "fieldname_with_sheet_nr",
          filter:=intersects($geometry, geometry(@parent))
                  AND x_max($geometry)=x_max(geometry(@parent))
                  AND y_max($geometry)>y_max(geometry(@parent)),
          concatenator:='')