Gwen Stefani And Her Son Apollo Pose With Blake Shelton For Sweet Birthday Photo

Gwen Stefani helped her youngest son celebrate his birthday, and she captured a sweet moment from the occasion on camera. On Friday, the 50-year-old No Doubt frontwoman took to Instagram to share a snapshot of herself and her boyfriend, country singer Blake Shelton, 43, posing with the birthday boy, Apollo Bowie Flynn Rossdale.

Apollo, Gwen's third child with her ex-husband Gavin Rossdale, turned 6 years old on February 28. In Gwen's snapshot, the little boy was smiling at the camera and sitting on Blake's lap. Apollo was wearing his wavy, chin-length hair parted to the side so that it covered up his left eye. He was rocking a black shirt featuring the yellow-and-orange flame logo of Thrasher, a skateboarding magazine.

Blake was sporting a dark blue collared shirt with short sleeves. The "Hell Right" singer usually wears a lot of product in his hair, but his salt-and-pepper mane was looking a bit untamed. Blake was also sporting quite a bit of facial scruff.

Gwen was standing up and leaning over to take a selfie with Apollo and Blake. She was rocking a top with black spaghetti straps, but her right shoulder was the only part of her body that was visible in the photo, save for her head. Gwen was wearing her platinum blond hair pulled back in a sleek ponytail. The "Hollaback Girl" star stayed true to her signature glam rock style by sporting a full face of makeup, an application including a smoky eye and a soft pink lip. Like Blake and Apollo, she had a big smile on her face.

Blake was holding Apollo's birthday cake up for the photo. The dessert was decorated with white icing and chocolate sandwich cookies. The words "Happy Birthday Apollo" were written on the sweet treat in rainbow-colored icing. In the caption of her post, Gwen called her son her "little angel boy."

Gwen's 9.8 million Instagram followers helped Apollo celebrate his big milestone by sharing their birthday wishes for him in the comments section of his mother's post. In the span of two hours, Gwen's adorable birthday photo garnered over 128,000 likes and 1,000 comments. Many fans mentioned Blake in their remarks.

"Happy birthday to Blake's little buddy," read one response to Gwen's post.

"Happy Birthday, Apollo! Blake's relationship with Gwen and her boys is just so precious!" wrote another fan.

"You are truly blessed by Blake. Especially since he gets to experience Apollo's bday. Your family has had such amazing journey, thank you for sharing," a third admirer remarked.

"Happy Birthday handsome little man," a fourth follower wrote. "He looks like Blake same eyes. Could pass for his biological father."

Blake has never had a biological child, but he has spent a lot of time bonding with Gwen's three sons. In fact, Blake has been a part of young Apollo's life longer than he has not; the little boy was 2 years old when Gwen and Blake started dating after meeting on the set of The Voice.

As previously reported by The Inquisitr, Gwen did describe herself and Blake as "parents" in an interview earlier this month, but it was in reference to Blake's sweet hound dog Betty, not her sons.