The former WESTLIFE star was so impressed by Carter's credentials - he's been hailed by Motley Crue rocker Tommy Lee as a top songwriter - McFadden persuaded the heart-throb to work his magic on his upcoming record.
A spokesperson says, "Brian called Nick out of the blue and asked if he could write for him for his next album.
"Nick liked the idea of working together and they've decided they'll hook up when he's in the UK for the Boys' sold-out tour in October.
"Even though Nick is in a boyband, he's done a lot of writing for other people and that stuff has a much harder edge.
"Brian knows his next record needs to sell and he's hoping Nick can help him."