The 28-year-old daughter of Sharon and Ozzy Osbourne has been dating vegan chef Matthew for the past two years, since meeting him at mutual friend Kate Moss' wedding back in 2011.
Matthew is the brother of singer Alison Mosshart, who makes up one half of The Kills alongside Kate's husband Jamie Hince.
Kelly and Matthew were rumoured to have become engaged just before Christmas, but Kelly later took to Twitter to deny the reports, writing: "Don't believe everything you read."
This time, however, she has confirmed the engagement news is correct.
Kelly hasn't shied away from publicly declaring her feelings for Matthew. She tweeted in June: "I'm in love and I don't care who knows about it!"
Matthew also joined the Fashion Police panellist on the set of a glossy photoshoot for Cosmopolitan magazine earlier this year, where Kelly said she'd never been more in love.
"He just wants to love me, and I just wanted to be loved by him. Every single other guy I've dated has wanted something from me," she said. "They'd call people I know and ask for favours. I'd have to say, 'Trust me. Telling someone you are my boyfriend isn't going to get you very far.'"
Kelly's not alone... check out some more engaged celebrity couples in our gallery below:
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