According to multiple sources, The Voice stars Blake, 41, and Gwen, 48, are determined to extend their family, Us Weekly reported.
The country star and pop-rock icon "will get married one day," said an insider close to Blake, "but right now they are hyper-focused on getting pregnant."
Gwen didn't learn she was expecting her youngest child, Apollo, until she was 43 years old, so the pair are confident they'll be able to conceive.
"They believe there is still a chance for Gwen," the Blake insider told Us. "They are incredibly hopeful."
Blake and the No Doubt frontwoman -- who is also mom to Kingston, 11, and Zuma, 9 -- met on The Voice in 2014 and began dating the following year after their splits from their respective spouses, Miranda Lambert and Gavin Rossdale.
Blake announced the end of his marriage to Miranda in July 2015, and Gwen broke it off with her husband of 13 years one month later.
By October of that year, The Voice couple felt comfortable enough to put their romance on display in public.
Part of the reason Blake and Miranda called it quits was reportedly due to his desire to be a dad, said another source close to the country singer.
So when he got together with Gwen, he was honest and open about his future plans.
"Blake told Gwen he does want kids of his own," said the source, "and Gwen was willing to try. With her, Blake has the exact relationship and family life he'd hoped to have with Miranda. Gwen's everything he wants."
A third Blake pal told the magazine, "Gwen and Blake started talking quickly about having a baby."
But the couple's dream has yet to be realized since they started trying for a baby in 2016.
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"Starting a family has not been easy for them," explained the insider. "It's something that they really want and it's just not working out the way they wanted it to."
However, the challenge isn't dividing Blake and Gwen, nor is it causing tension in their relationship.
"The struggle they're facing is making them stronger," noted the Blake insider. "They are so committed to one another and protective of one another."
Meanwhile, Gwen's family has been enjoying time with Blake in Oklahoma, where he owns a beautiful ranch.
"It's been a lot of fun for me to be the one to get to expose them to this," Blake told Entertainment Tonight late last month at the time his Tishomingo eatery, Ole Red, officially opened. "They love it so much, her entire family."
"There's times when we've had holiday gatherings," he added, "and I'm talking about 30-plus family members from her side, from my side."