Use wp_list_pages to display children links of one parent and one unrelated page

Hello,

I have a question about using wp_list_pages.

Here’s my dilemma:
I need to display all the children of one parent and then I want one page from another parent added to the same list. I need the unrelated page to be sorted alphabetically within the other links.

Here’s the code I currently have to display the children of one parent:

<?php wp_list_pages('title_li=&child_of=4608'); ?>

The page ID I need to add is 20898.

Any help is appreciated. My PHP skills are still at a pretty newbie level. ??