Gwen Stefani ''feels very secure'' with Blake Shelton.

The 49-year-old singer is set to celebrate her four-year anniversary with her country music star boyfriend later this year, and sources say the pair ''still act like lovebirds'', especially after Gwen landed a role as a coach on 'The Voice', where Blake also coaches.

Gwen - who previously worked on the singing competition for three separate seasons and first fell in love with Blake whilst on the show - is returning to replace Adam Levine after he announced his departure after 16 seasons, and the couple are said to be ''happier than ever'' now that they're working together again.

A source said: ''They're coming up on their four-year anniversary, but Blake and Gwen still act like lovebirds. They're really happier than ever, and being back where they first fell in love has been fun for them. They can't believe how quickly time has flown by, and their relationship is very solid. Blake worships her, and Gwen feels very secure with him.''

The 'Hollaback Girl' hitmaker often brings her sons - Kingston, 13, Zuma, 10, and Apollo, five, all of whom she has with ex-husband Gavin Rossdale - to set, who ''love'' getting to see their mother work.

Speaking to People magazine, the source added: ''It's like she never left. Her kids also love going to set.''

The comments come after it was recently claimed Gwen's romance with Blake, 43, is ''better than ever''.

A separate insider said: ''Gwen and Blake have been having the best time while shooting 'The Voice'. They laugh so much on set and backstage, and aren't shy about showing their affection and are better than ever.''

Gwen and Blake will be joined by fellow coaches John Legend and Kelly Clarkson when 'The Voice' returns to NBC in September.