The Irish heartthrob is on the road with the songwriter behind Justin Bieber's hit song 'Sorry' on his 'Flicker Tour' , and now they are planning to head into the studio together after forming a ''brother-sister'' like relationship.
Julia told the Daily Star newspaper: ''He's fantastic, we have this very brother-sister thing and tease each other the entire time, and act like we don't like each other although we love each other so much.''
The One Direction star previously revealed he'd love to work with Julia - who has also written for the likes of Fifth Harmony and Demi Lovato - as he is a huge fan of her.
He said: ''She's one of the best songwriters on the planet so I'll be looking to sit down and write with her.''
Niall is set to head back into the studio to start work on the follow-up to his hugely successful debut LP 'Flicker' - which came out in October - after completing his world tour, which comes to an end on October 3 at the INEC in County Kerry, Ireland.
Meanwhile, the 'On the Loose' singer recently recorded a performance of songs from 'Flicker' with a 45-piece orchestra.
The singer teamed up with conductor Gavin Murphy and the RTÉ Concert Orchestra for the unique performance last week at RTÉ Radio's Studio 1.
Niall commented: ''I made an album that came from the heart, my heart is in Ireland and I feel that there's no better way than to go on national television and play those songs with a 45-piece orchestra - and the RTÉ Concert Orchestra is one of the best in Europe, if not the world.''
The recording is set to be broadcast on RTÉ One sometime in May.
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