So sad to hear this. From the Associated Press:

Company spokeswoman Samantha Garrett said McQueen’s body was found in the morning but that she had no information “in terms of circumstances.”
Police did not directly comment when asked about how McQueen died, but said officers were called by the ambulance service at 10:20 a.m. (1020GMT) to an address on Green Street, in central London, and found a 40-year-old man dead. They did not name him but said next of kin had been informed.

The force said a post-mortem would be held but that the death was not being treated as suspicious.

Update: Alexander McQueen commits suicide: Britain has lost a great designer – and fashion ambassador