Blake Shelton is planning a fancy dress party for Gwen Stefani's 50th birthday.

The 43-year-old country crooner wants his partner to have a birthday she'll never forget this year - especially as it's such a milestone age - so not only is he whisking her away on vacation but he's also organising a big bash around Halloween for her.

A source told 'Entertainment Tonight': ''Gwen is turning 50 and she's over the moon about it. She feels confident in her age and she is completely in love.

''Blake wants to make her feel special.

''He's planning a big party for her, he is going all out! It's a costume party. Gwen is a huge costume lover. She has always loved dressing up for Halloween.

''Blake and Gwen have a lot to celebrate.

''They are both so incredibly happy in their relationship and in their lives right now. They have full open communication and truly appreciate one another. Gwen is always saying she has found her soulmate and best friend.''

The 'Hollaback Girl' hitmaker turned 50 on October 3 and Blake was one of the first people to wish her a happy birthday on his social networking sites.

He tweeted: ''Happy Birthday @gwenstefani!!!! I love you so much it's actually stupid... And possibly illegal in the state of California. (sic)''

And it seems the feeling is mutual as just a few weeks ago Gwen couldn't help but gush over the 'Voice' USA coach, whom she's been dating since 2015, during an interview.

She said: ''Life is full of surprises.

''I never thought in my wildest dreams, on paper, a cowboy and a ska-like girl from Anaheim would be hanging out but it works perfect. We're just having so much fun and we feel so blessed to be at this point in our lives.''

Gwen has three kids Kingston, 13, Zuma, 11, and Apollo, five, with ex-husband Gavin Rossdale.