The Rolling Stones star, 70, said: "I am still struggling to understand how my lover and best friend could end her life in this tragic way.
"We spent many wonderful years together and had made a great life for ourselves.
"She had great presence and her talent was much admired, not least by me.
"I have been touched by the tributes that people have paid to her, and also the personal messages of support that I have received.
"I will never forget her, Mick."
A spokesperson for the 70-year-old was forced to issue a statement late on Monday denying the couple, who were together for 13 years, had separated after a US website made a "horrible" claim that it was the breakdown of her relationship with Mick that drove L'Wren to suicide.
"The story in the New York Post re a split between Mick Jagger and L'Wren Scott is 100% untrue," said his spokeswoman, Victoria Scarfone.
"There is absolutely no basis in fact to this story. It is a horrible and inaccurate piece of gossip during this very tragic time for Mick."
L'Wren Scott was an iconic figure in the fashion industry and will leave behind an exceptional legacy.
The investigation into the 49-year-old's death is currently ongoing.