The saddest detail of Nicole and Keith's divorce can be found in their daughter's name.

Keith Urban's past comments about naming his daughter Sunday have taken on new significance following the news of his and Nicole Kidman's separation.

On Monday, it was announced that Kidman and Urban are separating after 19 years of marriage, with Kidman filing for divorce the next day. The couple share two daughters — Sunday Rose, 17, and Faith Margaret, 14.

A source told People that Kidman "didn't want this" and had been "trying to save things," with the pair reportedly living apart since the beginning of summer.

Watch: Nicole Kidman and Keith Urban at a Taylor Swift concert. Post continues below.

In a 2009 interview with Ellen DeGeneres, Urban explained how Sunday Rose got her name, making their separation all the more poignant.

"How did you come up with Sunday? Where did the name come from?" DeGeneres asked the country singer.

"We just love the name of the day. Particularly, when you don't have someone in your life, Sunday, in my experience, was the loneliest day. The day I dreaded the most. Everyone goes with their families, and if you don't have a family, you don't have anybody," Urban admitted.

He explained how meeting Kidman transformed his relationship with the day he once liked the least.

"It went from being sort of the most dreaded day of the week for us to being the most joyous day because we just had a family," he added.

Now, as the couple parts ways after nearly two decades together, their eldest daughter's name serves as a reminder of the day that brought them together.

According to court documents obtained by People, Kidman is seeking to be the primary residential parent of her and Urban's daughters. The couple have reportedly agreed to a parenting plan which gives Kidman 306 days with their daughters, while Urban will have 59 days.

They will continue to make major decisions regarding their children's education and health together.

Listen to Mamamia's daily entertainment podcast, The Spill, where hosts Laura and Tina explain what led to the split.

Feature image: Getty.