The 'Rolling in the Deep' hitmaker teamed up with the 'Chandelier' singer on a track titled 'Alive' and although it was originally intended for her highly anticipated third album, Sia has now kept it for her own record after Adele turned it down.
Sia said: "It's about [her] life, so now I sing the song from [her] perspective."
The 39-year-old singer went on to admit that a lot of the songs on her album 'This Is Acting' were originally written for other artists but for one reason or another had been rejected.
She told RTV Slovenija: "I have these songs made and they have [been] rejected, but [they] seemed good, so I kept [them for] myself."
Sia is now preparing to release 'Alive' as the lead single off of her seventh studio album.
Meanwhile, Adele is reportedly preparing to unveil her next LP, which is rumoured to be titled '25', in November after its original release date of May 2014 was pushed back by her record label XL Recordings.
The 27-year-old star's last album '21', which was released in 2011, sold 11 million copies worldwide and topped the charts in 2011 and 2012.