Hi BENOIT CHEVALIER,
RadRadioButton was designed to mimic the behavior of the standard Windows Forms RadioButton. For this reason there is not an easy way to group RadRadioButtons if they have different parent controls.
However, you might be able to achieve such a behavior through handling the ToggleStateChanged event of the RadRadioButtons. You should insert custom logic that resets the ToggleState property of the buttons in all other groups.
Let me know if I can assist you further.
All the best,
the Telerik team
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