Published Tuesday, 18 March 2014
L''Wren Scott, pictured with Rolling Stones frontman Mick Jagger. (© Getty)
The 49-year-old was found unconscious in her Manhattan, New York apartment, but was later declared dead by emergency services.
It is understood that police are treating the death as suicide.
Sir Mick, in a Facebook post on Tuesday, 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.
Sir Mick Jagger
"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."
Renowned fashion designer Scott had been dating 70-year-old rock star Jagger since 2001 after they met when she was the stylist at a photoshoot.
A short time after her death was announced on Monday it was revealed that her British fashion company had been losing money.
The Rolling Stones have announced they have pulled the plug on their entire tour of Australia and New Zealand, which was due to start on Wednesday, following the tragedy.
© UTV News