Facchinetti, 36, was hired last year to replace the house's founder, Valentino Garavani, who retired in January after 45 years of dressing royalty, first ladies and movie stars.
Facchinetti showed her second ready-to-wear collection for the house on Friday.
Italy's ANSA news agency quoted Facchinetti as expressing "bitterness" about the firing - which she said she learned of from news reports.
In a mocking reference to the label's statement, she is quoted as saying: "I thank the Valentino company for appreciating my 'creative contribution' and 'artistic refinement,' but I'm very sorry that such contribution and refinement were not exploited adequately."
She said she would leave Valentino feeling "strengthened as my work has been greatly appreciated in the world," the ANSA report said.
Facchinetti's newly announced successors, Maria Grazia Chiuri and Pier Paolo Piccioli, have been creating the accessories for Valentino for more than 10 years.
"We are very excited and honored by this opportunity," Valentino's statement quotes Chiuri and Piccioli as saying. "We will remain faithful to the fundamental values of the brand, while developing new ideas which fuse the heritage of the house with a more contemporary concept."
Garavani and his longtime business partner, Giancarlo Giammetti, welcomed the move and struck a parting blow at Facchinetti.
"There is an archive of thousands of dresses that one can draw from to be inspired and create a Valentino product that keeps up with the times," the retired designer was quoted by ANSA as saying. "Shame the one who came before them did not feel this need."
He praised Chiuri and Piccioli as "two serious and capable professionals" who have "always showed enormous respect and love for my work."
"I wish them the best of luck," he is quoted as saying.
The situation was reminiscent of events at Italian label Gucci three years ago. Facchinetti was replaced after just two seasons as the brand's women's wear designer. Her replacement was Frida Giannini, also an accessories specialist.