VBA code to Split and Sort String Values

Dear Excel Experts
I have a VBA code to loop through a column of 10K rows and store unique values in it. These unique values are basically years like 2018,2019,2020,2021 etc..

When i store unique values, the list is pretty much random like 2022,2019,2021,2018 etc (its because the original data itself is not sorted as per year.)
Is there any way that i can sort the data in ascending order of years after pulling unique values. I am adding this list to data validation later.

Dim unique_string
If Not InStr(unique_string, Cells(rloop, 3).Value) > 0 Then unique_string = unique_string & Cells(rloop, 3).Value & ","
 With Worksheets("Macro").Range("L13").Validation
        .Delete
        .Add xlValidateList, Formula1:=unique_string
  End With