Gwen Stefani and Blake Shelton have sparked rumours they've married in secret, after the No Doubt star was spotted wearing what appeared to be a wedding band.

The 51-year-old singer was spotted out and about with her country star beau in Santa Monica, California, on Saturday, and eagle-eyed fans were quick to point out that she was sporting a diamond band next to her giant engagement ring in the snaps obtained by the New York Post's Page Six.

Rumours about a secret wedding came just one day after Gwen was "kidnapped" by her family for an impromptu bridal shower - pictures of which she shared on her social media pages alongside the caption: "SHE’S GETTING MARRIIIEEEED.”

Despite Gwen's new accessory, Blake's hands were ring-free, and representatives for the pair have yet to comment on the speculation.

Blake, 44, previously told USA Today that he was taking a back seat when it came to planning their nuptials, because he knows his wife-to-be is going to do a fantastic job.

"I want her to do all of that stuff and handle it because it's going to be great," he said. "She's in the middle of planning the thing, and she's always so mindful … of me. She's like, 'Hey, I don't want to just take this thing over.' I think she's having a blast doing it. I mean, I know she's having a blast doing it."