The 31-year-old blonde actress jetted from New York to Mazan in the South of France for less than 48 hours to watch her 'Edge of Love' co-star ''shed tears of happiness'' as she tied the knot with The Klaxons keyboardist James Righton in front of just 11 guests on Saturday (04.05.13).
The mother-of-one was spotted leaving the leaving the Chateau Mazan where the married couple and wedding party were staying on Sunday morning and returning to the airport to fly back home to her fiance Tom Sturridge and their 10-month-old daughter Marlowe in New York.
Sienna previously revealed that she and Keira have remained close friends after bonding on the set of the film in 2008 and called the 28-year-old 'Anna Karenina' actress a ''timeless movie star''.
Keira and James exchanged vows shortly before midday at the town hall in Mazan, 67 miles from Marseilles, before speeding back to her family's nearby $5 million vineyard for their reception in a silver Renault Clio.
The actress wore a short strapless dress, reportedly the same Rodarte creation that she wore to a pre-BAFTA event in 2008, pale pink ballet flats, a cropped Chanel jacket and a delicate floral garland around her head.
Among the small number of guests at the ceremony included the actress's playwright mother Sharman MacDonald, father Will Knightley and Keira's brother Caleb, as well as James' father Nicholas and his brother Bill.
The rocker's bandmates were also among the 50 guests at the reception and provided the musical entertainment.
The couple got engaged in May 2012 after meeting through mutual pal Alexa Chung, but she is not believed to have been present at their wedding.