Here is a blog article that illustrates a similar scenario. I believe that you can easily adapt it to fit your needs. As a side note, please let me notify you that utilizing the Loaded event may no be a viable approach, due to RadGridView's container recycling mechanism (you can try PropertyChanged instead). As for your request to trigger it on StyleSelector.SelectStyle(), I believe it won't be a proper approach, as this would try to trigger the storyboard before the style itself has been applied. Please, let us know in case you need any additional assistance for the implementation of this.
the Telerik team
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