As Blake Shelton and Gwen Stefani continue to plan their upcoming wedding, The Voice coach has been building a strong bond with the blonde beauty's three kids — Kingston, 10, Zuma, 8, and Apollo, 2.

During a private tour at the Cincinnati Zoo & Botanical Garden on Aug. 8, "They really did look like a family," an onlooker told Life & Style. "Blake acted like he was Apollo's dad."

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And the boys, whose dad is Gwen's ex Gavin Rossdale, will play a major role in the couple's Christmas nuptials.

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Gwen and her kids.

“Apollo wants to be the ring bearer, and the two older boys will be junior groomsmen with Blake," an insider explained. "Blake wants it to be really special, to show them coming together as a family.”

According to the source, the country crooner will be paying for the entire wedding, which will be limited to family and close friends.

For more on Gwen and Blake’s whirlwind romance, pick up the latest issue of Life & Style, on newsstands now! And scroll through the gallery below for a look at the duo’s cutest photos.