Can I Remove Duplicates When Using CONCATENATEX

Hi

I am using CONCATENATEX to concatenate customer numbers from 1 column but using USERELATIONSHIP to point to another date column to ensure all the required customer numbers are being puled through.

However the DAX measure will return duplicate values and I would appreciate some assistance to be able to show only distinct values in this list.
Thanks for taking the time to stop by and read my query.

Here is the DAX measure I am using:

Customer.Nos = 
CONCATENATEX(
    TblIDRP,TblIDRP[Customer Number],
    ", ",
    TblIDRP[Customer Number],
    ASC
) & ", " &
CALCULATE(
CONCATENATEX(
    TblIDRP,TblIDRP[Customer Number],
    ", ",
    TblIDRP[Customer Number],
    ASC
), 
USERELATIONSHIP( TblIDRP[Date Trustee Decision Sent], DimDate[Date]))

As always, any assistance is greatly appreciated.

Paul