Do you Take That man to be your husband?
The singer, 36, is expected to tie the knot with Ayda Field, 31, on an island off the coast of California.
Williams' Take That bandmates - who he dramatically rejoined last month - were not attending the "intimate" ceremony on Santa Catalina.
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Hide AdAmong the guests said to be attending there wedding were his parents, and friend Jonathan Wilkes.
Los Angeles-based Williams and Field have been together for more than three years since meeting through friends.
They are reportedly going on a two-week honeymoon before he arrives back in the UK to promote the new Take That material. His previous girlfriends include model Rachel Hunter, pop star Nicole Appleton and actress Anna Friel.