<p>I want to make a .NET Form as a TopMost Form for another external App (not .NET related, pure Win32) so it stays above that Win32App, but not the rest of the apps running.</p>

<p>I Have the handle of the Win32App (provided by the Win32App itself), and I've tried <a href="http://msdn.microsoft.com/en-us/library/ms633541(VS.85).aspx" rel="noreferrer">Win32 SetParent() function</a>, via <a href="http://www.pinvoke.net/default.aspx/user32/SetParent.html" rel="noreferrer">P/Invoke in C#</a>, but then my .NET Form gets confined into the Win32App and that's not what I want.</p>

I think you're looking for is to P/Invoke
```
SetWindowLongPtr(win32window, GWLP_HWNDPARENT, formhandle)
```
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