Reporting Services :: Display Group Name Value Of Each Group In Column Header Outside The Group?

I have an SSRS 2012 table report with groups; each group is broken ie. one group for one page, and there are multiple groups in multiple pages.

'GroupName' column has multiple values - X,Y,Z,......

I need to group 'GroupName' with X,Y,Z,..... ie value X in page 1,value Y in page 2, value Z in page 3...

Now, I need to display another column (ABC) in this table report (outside the group column 'GroupName'); this outside column itself is another column header (not a group header) in the table (report) and it derives its name partly from the 'GroupName'  values:

Example:

Value X for GroupName in page 1 will mean, in page 1, column Name of ABC column must be ABC-X Value Y for GroupName in page 2 will mean, in page 2, column Name of ABC column must be ABC-Y Value Z for GroupName in page 3 will mean, in page 3, column Name of
ABC column must be ABC-Z

ie the column name of ABC (Clm ABC)  must be dynamic as per the GroupName values (X,Y,Z....)

Page1:

GroupName                 Clm ABC-X

X

Page2:

GroupName                 Clm ABC-Y

Y

Page3:

GroupName                 Clm ABC-Z

Z

I have been able to use First(ReportItems!GroupName.Value) in the Page Header to get GroupNames displayed in each page; I get X in page 1, Y in page 2, Z in page 3.....

However, when I use ReportItems (that refers to a group name) in the Report Body outside the group,

I get the following error:

Report item expressions can only refer to other report items within the same grouping scope or a containing grouping scope

I need to get the X, Y, Z ... in each page for the column ABC.

I have been able to use this - First(Fields!GroupName.Value); however, I get ABC-X, ABC-X, ABC-X in each of the pages for the ABC column, instead of ABC-X in page 1, ABC-Y in page 2, ABC-Z in page 3, ...