"Hello! can exclusively announce the safe arrival of @MrJackO & @lisamarstelly 's baby girl Pearl weighing 8lb 6oz. Love & congrats to them!" the magazine said in a Twitter posting.
Where and when the baby was born were not reported.
Osbourne and Stelly, 26, confirmed their engagement last year.
Ohio crash that killed two caught on camera [VIDEO]
Mena Suvari shares her delightfully awkward Christmas card photo