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."