The 'Fashion Police' host - who appeared in a 24-hour interactive video for 'Happy' which the singer made public last November - has been in the recording studio with the producer, but she hasn't given any details of the mystery project, other than to say she admired her collaborator's fashion sense.
She wrote on her blog: ''Recently I was in the studio pre-Grammy's with Pharrell Williams working on something... ;) he was wearing the infamous hat!
''If you know anything about my fashion sense you know that I am a huge fan of Vivienne Westwood!!!!! So naturally one of the first things out of my mouth was oh my god you are wearing my favorite Westwood hat. (sic)''
The 29-year-old star - who has previously released two albums, in 2002 and 2005 - first shot to fame appearing on 'The Osbournes' alongside her parents Ozzy and Sharon and brother Jack and has thanked fans for their support on the 12th anniversary of the programme's launch.
She wrote: ''To this day, it's been 12 years since the first episode of ''The Osbournes'' first aired!! WHAT A RIDE IT'S BEEN! Look at us THEN and NOW! thank you for all the love and support through the years xoxo (sic)''