The six-year-old was a flower girl for the young couple who tied the knot in front of 850 guests at St George's Chapel, Windsor Castle on Friday morning.
She sported a white bridesmaids dress with ruffled sleeves, complete with a colourful bow detail at the back and matching white tights.
Her hair was pulled back into a half-up up-do with white flowers fashioned in the crown as she showed off her royal-ready wave to onlookers.
Teddy was one of a handful of bridesmaids seen walking down the aisle behind the Princess when the ceremony began on Friday morning.
Viewers fawned over Teddy as they left the venue, where she was seen waving from a car window. One fan posted: "Omg your darling Teddy just adorable. So much like Robbie. You both look lovely x."
Another wrote: "Teddy has just made my heart melt. She looks absolutely adorable."
A third tweeted: "Teddy is a mini Daddy.!! She did so well today her little wave and smile was just perfect."
She joined Princess Charlotte, Isla and Savannah Phillips, Maud Windsor and Mia Tindall who were also flower girls.
Prince George was joined by Louis de Givenchy as page boy for the occasion.
Williams was in attendance with his wife Ayda Field who he also shares three-year-old son Charlton Valentine with and new-born daughter Colette Josephine.
Although Teddy managed to steal the hearts of the nation, Robbie failed to do the same after he was blasted for failing to help his mother-in-law Gwen Field retrieve her hat after it blew off on route to the Royal Wedding.
She fell victim to the windy weather which saw her navy hat take off and fly up the road behind her.
The former Take That star stood open-mouthed and failed to help as he watched his mother-in-law run after it.