"Twins!!!" one fan exclaimed.
"Wow those genes in your family!! Your mother and her girls gorgeous," remarked another.
"Lovely photo with ur lovely sister," a third penned.
In a 2017 chat with Show + Tell, Bec explained that she and Kate are as close as sisters can be, despite the fact that Bec and her family live in Melbourne whilst Kate and her brood are in Perth.
Bec's daughter Billie's middle name is also Kate as a tribute to her sister.
"During school and high school we used to fight so much - I think I've still got scars on my arm from cat fights with my sister. We used to drive each other bananas!" Bec confessed.
"I was the brain, Kate was the brawn so she'd be the physical fighter and I'd just lure her outside and then leave her and lock her outside for hours until Mum got home.
"We're close now but at times we hated each other."
Bec is married to former AFL star Chris Judd with whom she shares four children - eldest son Oscar (born in July 2011), daughter Billie (born in February 2014) and twin boys Tom and Darcy (born in September 2016).
"We have a date night every Wednesday," she revealed in her book, The Baby Bible.
"We book in the babysitter and Chris is really busy and so am I [but] even if it's just playing tennis, it's really important to have that time together."
The couple celebrated 10 years of marriage in December 2020.