"No column name was specified for column..." when aliasing results of CROSS APPLY

I have this table: from which I create this View: This view's CardId allows me to JOIN against the Card table with so I can retrieve the Count from any CardId. Here's my SQL:

SELECT * FROM (
    SELECT
        si.CardId SourceCardId,
        ti.CardId TargetCardId,
        (SELECT TOP 1 r.Name
        FROM dbo.Relationship r
        WHERE r.Id = rac.RelationshipId) [Name],
        Count(*) [Count]
    FROM dbo.Relationship_AcquiredCard rac
    JOIN dbo.AcquiredCard sac ON rac.SourceAcquiredCardId = sac.Id
    JOIN dbo.AcquiredCard tac ON rac.TargetAcquiredCardId = tac.Id
    JOIN dbo.CardInstance si ON sac.CardInstanceId = si.Id
    JOIN dbo.CardInstance ti ON tac.CardInstanceId = ti.Id
    GROUP BY si.CardId, ti.CardId, rac.RelationshipId
    -- you can probably ignore everything above
    ) X
CROSS APPLY
    (values (X.TargetCardId),
            (X.SourceCardId)
    ) whatdoesthisdo(CardId) --wut

What does whatdoesthisdo do? I got the CROSS APPLY from this answer . If I try to alias in the usual way, I get this error: Thanks!