Sharon Osbourne says witnessing the birth of her first grandchild has been "life changing".

The TV star's son Jack and his fiance Lisa Stelly welcomed daughter Pearl into the world on Tuesday. Sharon took to her Twitter page to gush about the family's new arrival.

"Today I witnessed my first grandchild being born, life changing experience. She is an angel (sic)," she wrote on her personal page.

Jack and Lisa's baby daughter weighed in at 8lbs. 6oz. and news of their family addition broke on the social networking site last night.

Jack's sister Kelly also tweeted her delight at the Osbournes' new addition.

"Today has been one of the most amazing days of my life! thank you so much for your congratulations but they realy should be gonig to @lisamarstelly & @mrjacko! I am one proud Auntie! (sic)" she wrote.

Sharon has previously revealed she can't wait to shower her grandchild with gifts.

"I'm going to be the absolute nightmare grandmother that is going to do everything wrong. I'm just going to spoil, spoil, and that's the job of a grandparent," she said.

Sharon - who wants Pearl to call her "Shazza" - joked it was an Osbourne family trait to be late, when the baby's due date was pushed back.

"Like it's Grandma, it's late. I'm always late and this baby is late... It could be [born] any second," she admitted last week.