Get Epic summary from sub-task key

I have a report by subtask and add a column to show the epic summary. I have used the following to get the epic link but not sure how to get the epic Summary.

[Issue].[Issue].GetMemberByKey(
[Issue].CurrentHierarchyMember.Parent.Key).Get(‘Epic Link’)

I tried the following but it did not return any results.

[Issue].[Issue].GetMemberByKey
(
[Issue.Sub-task].[Sub-task].GetMemberByKey(
[Issue].CurrentMember.key
).Parent.get(‘Epic Link’)
).get(‘Epic Name’)

EPIC---->Story-----Sub-Task