Fergie’s front-row spot will certainly be a stark contrast to Harry’s wedding, where she arrived alone and was seated at the back of the church, separated even from her children.
Sarah’s readmission into the royal fold is in many ways a direct result of the declining influence of the Duke of Edinburgh, who has made no secret of his loathing of her, and his desire to exclude her from all royal activities.
He has long refused to be in the same room as her, although the queen has been gentler, even inviting her to Balmoral in recent years.
But 97-year-old Philip will almost certainly end up having to swallow his pride and appear in a family photo with Sarah at the wedding.
Amazingly, this will be their first picture together in 26 years.
While the day will of course be focused on Eugenie, few would blame Sarah if she took a moment to quietly relish the final victory over Philip that her daughter’s marriage will give her.
The general public may not be enthused. But for the Kremlinologists and rune-readers of royalty, Eugenie’s wedding promises to be quite a day.