He also posted a solo portrait of the adorable animal chewing on a toy in a grassy field, captioned:
"Whatcha looking at."
Mum of the brood Victoria, meanwhile, shared an image showing eldest son Brooklyn holding little Sage, the pooch's perfect face pointed towards the camera to give fans and followers a front-on view.
"New family member Sage Beckham x," she wrote.
It's clear the whole famous family is totally smitten with sweet little Sage.
Romeo reposted one of his dad's snaps, adding "❤️ welcome", while Brooklyn shared his own puppy-love pic – a full-length outdoor snap in which he's cuddling the pup, while one of the family's other dogs – cocker spaniel Fig – watches on.
"New member to the family ❤️," Brooklyn wrote.
Speaking of Fig, she wasn't left out of the Christmas celebrations – and neither was Olive, the family's oldest doggo.
The pair of pooches were decked out in festive red-and-white doggy attire and looked like they were enjoying the holiday fun too, with Brooklyn sharing videos of them racing around the property and playing with their new pupper pal.
Just days earlier, on December 21, 45-year-old Victoria proudly announced that Cruz and Harper had been baptised. Actress Eva Longoria, 44, and singer Marc Anthony, 51, were among those named as their godparents.
“Proudest of days today watching Harper and Cruz being baptised in front of our friends and family 🙏🏻 So much to be grateful for x,” the former Spice Girl captioned a photo of her children on Instagram.
Tagging husband David, 44, the designer continued, “With love, VB x I love u @davidbeckham x.”
“I couldn’t be more proud of my children and thankful to my family, and the most wonderful Godparents 🙏🏻. We love you @evalongoria @kenpaves @marcanthony @davidgardner x kisses,” Victoria captioned a second snap.