The Hollywood heartthrob stunned the showbiz world after it emerged he had allegedly tied the knot with his actress girlfriend at a secret ceremony in Los Angeles last month.
A source told Britain's Daily Star newspaper: "Keanu and Autumn wanted something really low-key so opted for a quiet civil ceremony with only family and friends.
"They don't like causing a fuss. It was at a small restaurant in Los Angeles and was very simple and chic."
The smitten couple, who have been dating for just over a year, revealed their happy news after hitting the party circuit and introducing themselves as man and wife.
Last year Keanu, 40 and 39-year-old Autumn were believed to be planning to walk down the aisle after rekindling their romance 10 years after they first dated.
The 'Matrix' actor, who first dated Autumn in the early 90s, allegedly proposed over dinner in Los Angeles in August three months after they restarting their affair.
A source said at the time: "Commitment is a huge deal to Keanu.
"They have know each other for years. Over the last few months Keanu started thinking about settling down."
But the heartthrob star, who famously enjoyed a on-off relationship with British actress Amanda De Cadanet, has been beset depression and family problems in recent years.
Five years ago, then girlfriend, Jennifer Syme, gave birth to the couple's still-born baby, before being killed in a car accident a year later, while Keanu's sister, Kim, has been battling Leukaemia for several years.