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Kendall Jenner certainly wasn't a third wheel during a recent outing with the Biebers ... 'cause Justin and Hailey made her feel like part of the group by wrapping her up in a threeway embrace.

The trio were spotted at the Dijon show in San Diego Saturday night vibing to the music in a super famous sandwich formation ... Kendall in front, Hailey directly behind her, arms curled around Kendall's stomach.

Justin's in the back holding them all together in one big bear hug ... while all they gently sway to the dulcet tones of Dijon's voice.

The three broke apart in another clip ... and Justin ran his fingers through Hailey's hair -- just Hailey here -- while Kendall sat alongside them. Still, it was clear the three were feeling super connected in their friendship

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