The jailbird, 26, hired celebrity lawyer Henri Brandman after seeing snaps of the singer cuddling up to Josh Bowman, 21, on the Caribbean island of St Lucia.
I can confirm that I have been instructed to commence divorce proceedings on the grounds of adultery, says a statement released by Henri.
It is thought Blake could seek half of his 25-year-old wife's £10million fortune.
'Papers have been received and the matter is with Amy's lawyers, says her spokesman.
Where to next?
Divorce - what do I do first?
Divorce: How and when to tell the kids
Fun and win:
What stage is your relationship?
Celebs and their tattoos