The control which is most suitable for that purpose is a RadWindow which is used with its NavigateUrl property set to the desired url. After that you can have a link/button/etc. on every page which is loaded and when clicked - change the url so that the new page is shown in the RadWindow. In addition, radWindow has PI which allows pin functionality, maximize, minimize, close, AutoSize, etc which will be also useful in your case.
One similar demo which shows an image gallery and AutoSize functionality is the following one:
When you click an image, it is loaded in the adjacent RadWindow, you could organize this logic e.g in a button inside a page, etc.
I also suggest to examine the other demos for RadWindow to get a better understanding on its capabilities.
I hope that my suggestion and explanations are detailed enough and helpful, let me know if you have additional questions.
the Telerik team
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