Spending time with Gwen Stefani's children has made country star Blake Shelton realise he's "missed out on a lot" by not having kids of his own.

The Boys 'Round Here hitmaker began dating Gwen in the autumn of 2015, not long after he divorced singer Miranda Lambert and the No Doubt frontwoman called it quits with her rocker husband Gavin Rossdale, the father of her three sons: Kingston, 11, Zuma, nine, and Apollo, four.

Their relationship has continued to grow from strength to strength, and Blake admits he would never have envisioned himself so happy to be surrounded by kids, especially as the 41-year-old thought fatherhood just wasn't on the cards for him after two failed marriages.

"I never saw that coming, but they're so fun," he shared on breakfast show Today. "They are (great kids)... and at this point in my life, I kinda had put that (fatherhood) one side, like, 'Well, I guess that wasn't meant to be,' or whatever, then all of a sudden it happens one way or another, (and) it's like, 'Wow, I've missed out on a lot,' so having them around is... so much fun."

Blake, who was previously married to Kaynette Williams from 2003 to 2006, is also still in disbelief at being able to call pop beauty Gwen his girlfriend, insisting he is so in love with her.

"Of course, how could I not be (in love with her)...?," he gushed. "She is the greatest."

Gwen has frequently made it clear the feeling is mutual, and it appears her extended family members are big fans of Blake too.

Over the weekend (17-18Mar18), she posted a short video clip on Instagram of her aunt Donna giving her a little love advice as the Stefani family celebrated her 90th birthday.

"Don't get rid of that wonderful boyfriend of yours," Donna tells the singer, who replies, "I'll try not to!".

Gwen, 48, sent the sweet message directly to Blake, who was unaware it had also been shared with the world.

"I didn't know that was on her (Instagram), 'cause she just texted me that," he admitted on Today. "I thought it was just (between us), I didn't know she put it (online)."

However, he has no issues with Gwen giving fans an insight into their romance, quipping, "As long as it's positive like that, I agree with what she (Donna) is saying!"