Fiona's crew snatches Stacy at the concert reception
Reggie spills a drink on Stacy, posing as Margaret, Mindy leads her to the ladies' room, and Fiona springs her switch.

Stacy De Novo in 3 The Princess Switch films, every moment in release order.
49 moments · 1h 43m · by Favseen
Moments 31–49 of 49
Reggie spills a drink on Stacy, posing as Margaret, Mindy leads her to the ladies' room, and Fiona springs her switch.
Fiona, posing as Margaret, fumbles an Oxford reunion; Stacy insists to Reggie and Mindy they kidnapped the wrong person.
Stacy hides, gives Reggie and Mindy the slip, and Edward and Frank arrive in time; the reunited couple make promises.
Mid-oath, Margaret and Stacy burst in; Fiona blames Antonio, and Margaret gives her first royal command.
Margaret, still dressed as Stacy, chases Kevin to the gate, explains it was Fiona, and Kevin asks her to marry him.
Margaret asks a passing officiant to marry them on the spot; they improvise vows as his flight is called.
On Christmas Day, Margaret takes the oath in full and is crowned to cries of long live the Queen.
Mid-rehearsal, Margaret and Stacy learn the Vatican's relic vanished from a guarded vault: drugged guards, wiped drives, no leads.
Edward's unhelpful Belgravia jewel story, then Stacy pitches a crooked insider and Margaret names her cousin Fiona; Kevin vows to nail things down.
Hacked Interpol files and a drug trail lead Peter to billionaire collector Hunter Cunard; the only option is a heist at his Christmas party.
With Reggie sprained, Frank suggests the queen impersonate Fiona; everyone scoffs until Margaret nails Fiona's voice.
Margaret debuts her Fiona disguise beside the real Fiona, and the room finds the match amazing and a little unsettling.
Mother Superior calls: Fiona's hearing moved to tonight. With Fiona at the heist, Stacy decides to impersonate her, and Edward joins.
In Fiona's heels Stacy flounders before the committee while Edward testifies; she oversells it by asking for a longer sentence.
Stacy confesses her convent switch, the crew regroups, then Fiona unwraps the Star and realises Peter swapped it.
Kevin and Olivia walk in on look-alikes; a kiss settles which is Margaret. Fiona hears her sentence is gone and picks Capri.
Fiona hands the polished Star to the cardinal and Moretti, Margaret welcomes Fiona and Bianca as family, and Stacy forces a hug.
Margaret and Stacy open the ceremony and hand the honor to Olivia; the giant tree and the Star of Peace light up.
An upbeat Christmas number gets the whole celebration dancing after the lighting.