The Queen's granddaughter looked besotted with her newborn as she doted over him during a low-key appearance at the Cirencester Park International Horse Trials.
Zara - who shares Lucas and daughters Mia, seven, and Lena, two, with her husband Mike Tindall - was at the event to support her horse Classicals Euro Star, ridden by equestrian Jason Wood on the day.
WATCH: Mike Tindall reveals birth of baby boy on his podcast
Wrapping up in a comfy-looking jacket by The North Face, jeans and a pair of boots, Zara blended into the crowd, hiding behind a baseball cap and sunglasses.
In photos obtained by Mail Online, Zara was spotted chatting to other spectators as she pushed Lucas around the park in his pram.
Last week, Zara's husband shared an update on their five-week-old son. Speaking on his podcast The Good, The Bad & The Rugby, he told co-hosts Alex Payne and James Haskell: "There's not much going on. Just newborn, a month-old, same old stuff. Feeding, bum wiping, but otherwise all good."
Mike and Zara are also proud parents to daughters Mia and Lena
Mike announced the birth of the couple's third child during an episode of his podcast last month and revealed his son was born on the bathroom floor.
"Sunday got even better because a little baby boy arrived at my house," Mike said. "Arrived very quickly. Didn't make it to hospital. On the bathroom floor. So yeah, it was running to the gym, get a mat, get into the bathroom, get the mat on the floor, towels down, brace, brace, brace.
The North Face Quest Jacket, £100, Cotswold Outdoor
"Fortunately the midwife who was going to meet us at the hospital wasn't that far away so she drove up just as we had assumed the posit (position) and the second midwife arrived just after the head had arrived," Mike added.
A spokeswoman for the couple later confirmed: "Zara and Mike Tindall are happy to announce the birth of their third child, Lucas Philip Tindall. The baby was born at the couple's home in Gatcombe Park on Sunday 21 March, weighing 8lbs 4oz."
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