Tab order of close button in popup with tab panel

My first post here. I am sure it won't be the last.

I am developing an accessibility prototype which features a popup tab panel.

I followed the recommendations at https://www.w3.org/TR/wai-aria-practices-1.1/#tabpanel and it works very well with both keyboard and mouse.

What I am now looking for is a recommendation for how to go from the tab list to the close button via keyboard control.

The recommendations call for the tabs to be selected in a loop, i.e. when you tab off the last tab, the first tab gets selected and vice versa, with "Home" selecting the first tab and "End" selecting the last.

Is there a 'best practice' for closing the popup tabbed panel?

Would it be misleading or very wrong to map "End" onto its close button? Is there another key which would be more suitable? I think we will be using "Esc" for something else.

Thanks in advance.