And less than a day later, the 34-year-old shared an extra pic - this time of herself cradling her newborn.
In the pic, little Henry's is seen sleeping peacefully - with a button nose and brunette whisps of hair, he really is ridiculously cute.
Doting dad Pete also shared another gorgeous video of his son lying in the hospital.
"Henry George," Pete wrote.
"The newest littlest member of our squad of four, led by my hero - @sylviajeffreys 💕"
In the gorgeous video, Henry gazes up into the camera looking curious (and did we mention adorable?).
It's an exciting step for the pair, who also share an elder son Oscar, who is one.
Speaking to The Weekly in March, Sylvia chatted about her joy in having a family of boys.
"When we tell them our boys will be 14 or 15 months apart, they roll their eyes and say, 'Good luck!' But the silver lining is that, with the world being the way it is right now, we're not missing out on anything being stuck in the baby bubble. So we may as well stay here in the zone and ride it out," she said at the time.
"I love the idea of being a boy mum because I was a tomboy as a kid, very sporty, and I like the idea of rumbling around with a couple of boys."