Sharing the news online, the Transformers actress said the couple have “walked through hell together”.
She posted an intimate video on Instagram, showing the US rapper, whose real name is Colson Baker, getting down on one knee to propose while Fox covers her face with her hands.
She captioned the video: “In July of 2020 we sat under this banyan tree. We asked for magic.
“We were oblivious to the pain we would face together in such a short, frenetic period of time.
“Unaware of the work and sacrifices the relationship would require from us but intoxicated off of the love. And the karma.”
She added: “Somehow a year and a half later, having walked through hell together, and having laughed more than I ever imagined possible, he asked me to marry him.
“And just as in every lifetime before this one, and as in every lifetime that will follow it, I said yes.
“… and then we drank each other’s blood.”
Posting on his Instagram account, Kelly showed a close-up of the ring he had designed by British jeweller Stephen Webster for the occasion.
He wrote: “Yes, in this life and every life. Beneath the same branches we fell in love under, I brought her back to ask her to marry me. I know tradition is one ring, but I designed it with Stephen Webster to be two: the emerald (her birth stone) and the diamond (my birth stone) set on two magnetic bands of thorns that draw together as two halves of the same soul forming the obscure heart that is our love. 1-11-2022.”
Fox has previously described herself as “unusual” and once said she “went to hell for eternity” after taking a powerful hallucinogenic in Costa Rica with her now-fiancé.
The couple recently appeared on the cover of British GQ Style’s Autumn/Winter 2021 issue.
Fox told the magazine she has met her “soulmate”.
The Hollywood actress was previously married to 90210 star Brian Austin Green, with whom she has three children.