Unfortunately, the rotation axis cannot be controlled - the origin of the rotation is the label center. You can use the labels position to achieve similar results:
|<LabelAppearance RotationAngle="-45" Position-AlignedPosition="TopLeft" >
The results however will vary according to the label text length - the longer the text, the farther the right end will go. I hope this workaround is applicable.
the Telerik team
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