Gwen Stefani's son is looking like Blake Shelton's twin! The "Hollaback Girl" hitmaker posted an Instagram tribute for her middle son Zuma's 17th birthday Thursday, Aug. 20, and one sweet snap features the star's son with his famous stepdad.

Gwen Stefani and Blake Shelton‘s marriage is reportedly on rocky grounds. A source exclusively told RadarOnline that the country star is leaning on friend Keith Urban for marriage advice after hitting a rough patch with his wife.

Gwen Stefani celebrated her "sweet and talented" middle son Zuma this week with a special post on social media. Zuma turned 17 on Thursday (Aug. 21), and the proud mom of three boys marked the occasion by sharing a series of photos and a video of her son strumming on a guitar and singing.