Meghan Markle did not attend Pippa Middleton's wedding to James Matthews.

This is a fact.

But the rumored reason why Markle skipped the festivites is now causing Royal Family followers to put down their drinks, stop operating any heavy machinery and ask one simple question:

Wait... WHAT?!?

According to the new unauthorized Markle/Prince Harry biography, "Finding Freedom," Markle pulled out of Middleton's big day because she didn't want to "create a media circus" and because she was afraid reporters would NOT focus on anything related to Pippa's wedding.

Instead, she was worried they'd be busy comparing her and Pippa's rear ends.

For real.

The authors of this book claim, at least.

If you'll recall, Pippa's backside sort of stole the show at her sister's wedding to Prince William.

Seriously, all anyone wanted to talk about afterward was Pippa Middleton's butt.

In this latest case, Markle was going to attend Pippa and James' ceremony, and purposely selected an "unflashy gown" for the occasion in order to avoid any kind of paparazzi scrutiny.

She “put careful thought into her outfit” to make sure it was “stylish without being splashy,” the book says.

HOWEVER...

... with mere hours to go, the then-Duchess decided not to attend when The Sun newspaper ran a cover story with a headline suggesting it would be “Meghan v Pippa” in the “Wedding of the Rears,” the biography alleges.

The authors detail how Carole Middleton and Pippa "reluctantly" invited Meghan to Pippa's Berkshire wedding in May of 2017, yet "privately harboured concerns" that her presence alongside Prince Harry would "overshadow" the main event.

To be clear, of course, neither Markle nor Harry told the authors this.

By their accounts, neither contributed in any way to this controversial book.

The former Suits actress reportedly checked into a nearby Airbnb on the day of the wedding, while her husband  went to the church service alone.

Markle then later snuck into the reception in a “decidedly unflashy long black gown” and having done her own makeup, the book says.

Ironically, Markle’s then-best friend, Jessica Mulroney, ended up garnering major headlines... thanks to a rear shot of her in a figure-hugging blue gown.

For those who forgot, meanwhile, here's a look at Pippa from behind at Kate and William's wedding:

Finding Freedom claims to offer fresh insights into Harry's falling out with William and how the Harry and Meghan felt "thrown under the bus," after disagreements that started when William referred to Markle as "this girl" and voiced concerns that he might be rushing the romance.

The author' note appears to acknowledge that the writers worked with the couple on the biography, reading:

"We have spoken with close friends of Harry and Meghan, royal aides and palace staff (past and present), the charities and organisations they have built long-lasting relationships with and, when appropriate, the couple themselves."

Thus far, however, Markle has not confirmed that concern over her butt being compared to Pippa's butt was the basis for her wedding snub.