Katharine Mcphee and David Foster "argued a little bit" over their new single.

The 39-year-old singer and David, 73, have recorded a new version of 'Amazing Grace', and Katharine has revealed that the married couple had a "debate" before they agreed to put the song on their new album.

The singer - who is set to release the second part of their 'Christmas Songs' album later this month - told 'Entertainment Tonight': "We argued a little bit, not in the bad way. It’s a bit of a debate over whether we should do ‘Amazing Grace’ because I said, 'It’s not a Christmas song, it’s a religious song.'

"The label ended up actually really liking it because we’re using it as our first single to kind of get out there, kind of earlier before the whole Christmas craze without it beating you over the head that it’s a Christmas song. So it’s actually kind of cool that we did it."

The loved-up duo have also toured together this year, and they've relished performing with each other on stage.

David said: "It’s been great."

Despite this, Katharine admits that it hasn't been entirely straightforward.

The singer confessed that she's already grown weary of the constant travelling.

The brunette beauty - who competed on 'American Idol' back in 2006 - said: "Being together has not been the shlep. Just the constant packing and unpacking.

"You wake up in a new city every day and it’s just a grind. That’s the only part that sometimes wears on you. And you just want to be in your own bed. But when we’re on-stage for those two hours it’s the best part of the whole thing."