britney chairBritney Spears has joined the long list of popstars working with Sia.

Last night the '(I've Just Begun) Having My Fun' hitmaker tweeted: "Had an AMAZING writing session today with the beautiful and talented @Sia. We wrote such a special song together :)".

':)'.

Three hours later — she was probably busy writing eight more songs — Sia tweeted: "Oh gosh miss @britneyspears is the sweetest. Very special day."

How lovely.