Kelly Osbourne bought her mother a diamond ring for her birthday.

The 25-year-old star enjoyed a low-key Celebration with Sharon Osbourne - who turned 58 earlier this month - and surprised her famous parent with the sparkling band and a sweet treat.

Writing in her Closer magazine column, Kelly said: "I couldn't figure out what to get my mum because she's one of those people who will just end up buying something for herself if she really wants it. I ended up getting her the most beautiful ring with a moonstone and diamonds. I also surprised her with a cake from a Los Angeles bakery called Sweet Lady Jane's. They make this amazing berry cake that people here are obsessed with - it's decorated with flowers and vines made out of icing. We spent the night in, just the two of us - it was low-key in the best of ways."

Kelly and Sharon - who is married to rocker Ozzy Osbourne - are so close they even exercise together.

Kelly - who lost a considerable amount of weight during and following her appearance on TV show 'Dancing With The Stars' - recently revealed: "Mum's started to work out with me and my trainer, Sarah Hagaman. She loves it.

"My weight loss has been healthy and gradual. I haven't gone to extremes - it's just been down to smart eating and regular exercise."