Kelly Osbourne rang in her 41st birthday -- her first without dad Ozzy Osbourne -- with family at Los Angeles' historic Chateau Marmont.

Check out the clip of her heading into the posh hotel ... she appears to be in high spirits as she holds her nearly 3-year-old son, Sidney , close on her hip while her Slipknot DJ fiancé Sid Wilson gets their stroller together. Gallery Launch Gallery Backgrid

She showed off her frame in a fitted black dress and drew attention to her famous cheekbones by putting her platinum blonde hair in a ponytail. Backgrid

The "Fashion Police" alum was joined by her family -- including mom Sharon and brother Jack -- for her special night out. Backgrid

As we mentioned, Kelly celebrated her first birthday without her father Monday ... and he

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