The fashion designer - who committed suicide last week - has reportedly left her entire fortune to her grieving lover, whom she dated for 13 years.
In addition to her lavish $8 million New York condo, L'Wren has also given Mick, 70, all of her expensive jewellery, clothing and all of her cars.
In the will, obtained by the New York Post newspaper, she wrote: ''I give all my jewellery, clothing, household furniture and furnishings, personal automobiles and other tangible articles of a personal nature ... to Michael Philip Jagger.''
The will was signed by the 49-year-old ex-model on May 23, 2013, in Beverly Hills, California.
L'Wren also insisted she was ''intentionally'' ignoring her siblings - including sister Jane Shane, 53, who she hadn't spoken to in six years - in her will.
The news is surprising as she had made her older brother Randall Bambrough, 58, co-head of her fashion company LS Fashion Ltd. just last year.
She wrote in the will: ''Except if otherwise provided in this will, I have intentionally omitted to provide herein for any of my heirs living at the date of my death.''