Blake Shelton reportedly asked Gwen Stefani's sons for their permission before proposing to her last month.

The country music star and No Doubt frontwoman, who have been the subject of marriage rumours for years, announced their engagement on Instagram and later told fans they were "extremely excited" about their upcoming wedding.

But before he popped the question, Blake apparently wanted to make sure Gwen's three boys - Kingston, 14, Zuma, 12, and Apollo, six - were happy with him officially becoming their stepfather.

"Blake told her boys that he wanted to propose and asked their permission," a source told People. "Her family very much approves of him. He's an amazing partner and a great extra dad to the boys. Gwen is ecstatic. The proposal was a surprise."

The marriage will be the second for Stefani, 51, who was wed to Bush frontman Gavin Rossdale - the father of her three sons - from 2002 until they finalised their divorce in 2016. Meanwhile, it will be 44-year-old Blake's third trip down the aisle, after unions to Kaynette Williams and second wife Miranda Lambert.

Gwen and Blake started dating in 2015 after meeting on the set of U.S. TV show The Voice.