Fergie, 58, sported a suit-style dress for the occasion, waving happily to the crowd as she made her way to St George’s Chapel.
The Duchess accessorised her look with a hat worn at a jaunty angle – and covered in lace detailing.
Blue appeared to be a colour choice that was in vogue for the occasion - as Victoria Beckham and Fergie's daughter Princess Beatrice also wore shades of the hue.
Earlier in the week, the UK’s Daily Express reported that Fergie, 58, had suffered a wedding ‘snub’.
While she was on the guest list for the wedding ceremony, it was said she would not be attending the evening reception.
In the days leading up to the event, she was pictured at St James’ Palace enjoying herself – before posting pictures on Instagram of herself in Yorkshire.
Once inside St George’s Chapel, the Duchess spent time greeting others – kissing several people on the cheek.
Other A-list wedding guests used the time before the nuptials to chat excitedly amongst themselves.
Idris Elba, George and Amal Clooney, Serena Williams and James Corden were seen greeting each other, and talking at length while they waited for the ceremony to begin.
The Beckhams and Sir Elton John also spoke to the other well-known faces amongst the congregation.