Lily Allen and her sister Sarah Owen arguing "for years"
The siblings are currently business partners after opening a clothing shop and designing a fashion line - both called Lucy in Disguise - together and although the pair love working together, they still have the occasional argument.
Lily told Irish TV show Xpose: "It has its ups and downs. I think in any start up business it`s stressful and that just gets multiplied by the fact that we know how to argue, we`ve been doing it for years but it`s equally as rewarding when really good things happen because you feel like you`re sharing it with somebody who understands. It`s great."
Lily and Sarah - who share the same mother, Alison Owen - were not close when they were younger and Sarah, who is older by five years has previously blamed their personality clash on the age difference.
She said: "I`ve spent a lot of time feeling frustrated because I`m not particularly amazing at any one thing.
"I think Lily was angry at me for a lot of the stuff that happened in our childhood. I`m five years older so I was having my whole teenage experience just as Lily was forming her opinions.
"She was not the little sister I expected at all. When mum was pregnant I thought I was going to have an adoring sister who wanted to be guided by me.
"But it became clear really early on that Lily was a fiercely independent spirit who would take guidance from no one."