The ex Spice Girl, 46, is well known for rarely smiling when on camera or out and about in public.
But on Instagram earlier today (Tuesday, May 26), Cruz posted a throwback of himself with his mum, apparently enjoying a spa day together.
What was in the picture?
In the pic, Victoria - who took the picture of them in a mirror - is beaming for the camera, showing off her pearly whites.
Cruz highlighted the fact in his caption. He wrote for his 1.7million followers: "Apparently my mum does smile."
And dad David couldn't resist using it as an opportunity to poke fun at his wife.
He featured in the comments, where he took aim at the brightness of her teeth by comparing her to Friends character Ross Geller.
"How white are mum's @Victoriabeckham teeth?" David asked, adding with a laughing-crying emoji: "It's Ross from Friends."
The comment is a reference to an episode of Friends in which paleontology professor Ross goes on a date and realises, too late, that his teeth are so white they glow in the dark.
How did his fans react?
David's fans were in hysterics. One warned: "You're in trouble!"
Another agreed: "Oh my god yesss."
A third called his comment "savage".
Victoria is currently spending the lockdown with David and their three youngest children - Romeo, 17, Cruz, 15 and Harper, eight.
Their eldest, 21-year-old Brooklyn, is isolating away from the family in the US with his girlfriend, Nicola Peltz.
Posh wrote about missing her oldest son on America's Mother's Day earlier this month. She said on Instagram: "Happy Mother's Day to all the mothers celebrating and being celebrated around the world today.
"As is the case for so many I cannot wait for the time when I can be reunited with all my family. I miss you @brooklynbeckham. Kisses."
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