Mick Jagger, L'Wren Scott

Mick Jagger is speaking out about the suicide of his longtime girlfriend, fashion designer L'Wren Scott.

"I am still struggling to understand how my lover and best friend could end her life in this tragic way," the Rolling Stones singer posted on his Facebook page Tuesday, along with a photo of Scott. "We spent many wonderful years together and had made a great life for ourselves."

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Scott was found dead in her Manhattan apartment Monday morning from an apparent suicide. A spokesperson for Jagger has called reports that the couple split before her death "100 percent untrue."

Scott's clothing was worn by celebrities including MadonnaMichelle Obama and Angelina Jolie, and was also sold in Barneys and Banana Republic. On Tuesday, the New York Post reported that Scott's company was nearly $6 million in debt at the time of her death.

"She had great presence and her talent was much admired, not least by me," Jagger wrote. "I have been touched by the tributes that people have paid to her, and also the personal messages of support that I have received."

Added the singer: "I will never forget her."

The Rolling Stones were supposed to launch an Australian tour Wednesday, but have postponed the concert dates indefinitely amid news of Scott's death.