Madonna ''knows she can be difficult'' to work for.

The 'Hung Up' hitmaker admits her ego is ''out of control'' sometimes but says that is to do with her zodiac sign.

In a preview clip from her 'Madonna: Rebel Heart Tour' documentary, she said: ''I know that I can be difficult and demanding and push you, and sometimes my ego is out of control but I am a Leo.''

And the 58-year-old singer previously revealed she thinks it is too ''easy to become famous'' and that has caused some musicians to become too ''focused on fame''.

She said: ''I was already famous before social media, so for me fame isn't the burden. Fame is the manifestation or the by-product of my work, and that was two decades before social media. Now to me the burden is people are more focused on fame than actually doing the work or being an artist. Now it's easy to become famous. What isn't easy is to develop and grow as an artist without being distracted or consumed with fame.''

Meanwhile, Madonna - who has Lourdes, 20, Rocco, 16, David, 11, and Mercy, 10 - previously compared herself to renowned artist Picasso.

She explained: ''I like to compare myself to other kinds of artists like Picasso. He kept painting and painting until the day he died. Why? Because I guess he felt inspired to do so. Life inspired him, so he had to keep expressing himself, and that's how I feel ... I don't think there's a time, a date, an expiration date for being creative. I think you go until you don't have any more to say.''