David Foster and Katharine McPhee on Coping With the Death of Their Nanny, Talk New Music (Exclusive)

The couple's nanny, Yadira Calito, was killed after an accident in August.

David Foster and Katharine McPhee are still working through their grief. In August, the couple's nanny, Yadira Calito, was killed following an accident

"It's been tough for her," Foster tells ET in a joint interview with McPhee. "Yeah, it's been tough. She's managing."

"Thank you," McPhee adds. 

On Aug. 11, McPhee shared that she would have to leave her and Foster's Hitman Tour early, following a "horrible tragedy." 

Days later, the LAPD shared that Calito was a customer at the Hamer Toyota dealership service center in Mission Hills, California, when an 84-year-old woman crashed her Toyota RAV4 into the building, causing major damage and colliding with several people inside. Two employees, ages 23 and 35, were transported to a local hospital with non-life-threatening injuries. Calito, 55, sustained fatal injuries in the crash. She was pronounced dead at the hospital. The driver was not injured in the collision.

In the month following, the pair have returned to the road and are also in the process of making music for the holidays. The latest release will be the continuation of Christmas Songs

"We got a nice response from the first seven songs so we thought, 'Oh, people are kinda digging this," Foster says.

"Volume two, we'll just complete the whole thing," McPhee adds. "A couple of my girlfriends are like, 'You're doing another Christmas album?' I'm like, 'No, this is a completion of the first Christmas album.'"

For Foster, who has been in the music industry for decades, creating music for the holidays comes easy, as he knows that he can take a song and flip it in any way.

"Believe it or not it's always fresh," Foster, who has done holiday albums with Josh Groban, Michael Bublé, Celine Dion and more, says. "Like, you could give me a song title right now of a Christmas song, I'd go to the piano. I could do it probably thee or four different ways without really thinking about it. In a jazzy way, in a country way, in a classical way, in a slow way, in a fast way. And so I just mix it up."

For McPhee, she gets to work with her husband, which makes the experience fun for her.

"It's pretty fast and furious 'cause he gets so focused," she says about her husband's producing. "There's not a lot of messing around. It's like you see the back of his head for a lot of the day honestly 'cause he just drills down. But for me, my favorite part is obviously being in the recording booth when he's recording my vocals. I don't see anybody, but I just hear his voice and he's always been the best to record vocals."

Foster and McPhee's first single, "Amazing Grace," will be out Oct. 6 and Christmas Songs will be out Oct 20.