Say it ain't so!

Though Kate Middleton is "absolutely delighted" her younger sister, Pippa Middleton, is engaged to hedge-fund manager James Matthews, a royals expert has revealed the Duchess of Cambridge surprisingly may not be included in Pippa's wedding.

According to author Judy Wade, Kate, 34, might skip her 32-year-old sibling's nuptials because she wouldn't want to overshadow the bride.

pippa middleton

Kate (left) and Pippa (right) at Kate's 2011 royal wedding.

"Kate would upstage her sister," Wade told [People](http://www.people.com/people/package/article/0,,2039522221019391,00.html)_. "It's a tricky situation for Pippa. She would want her sister by her side, as who else would she trust to make things go well?"

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"But if your sister is a future Queen, she is going to upstage the bride and draw attention. Kate would want to be in the background as much as possible," she added.

Click through the gallery below to see Kate and Pippa’s cutest sister moments!