Eliza mentioned their journey to pregnancy wasn't "smooth sailing" in her caption, alluding to the miscarriage she suffered in 2019.
Speaking at a convention in Vancouver in February 2020, Bob and Eliza revealed they had lost a pregnancy shortly after they married the previous year.
They had been filming The 100 at the time and though the loss was heartbreaking, the couple said they had plans to try to start a family again.
Bob also revealed that he had gotten a tattoo in memory of his and Eliza's unborn child.
Now the pair couldn't be happier to finally announce that they're expecting again, though chose not to reveal how far along the pregnancy is.
Though the couple started out as Aussie soap actors, it wasn't until they were both cast on the CW sci-fi drama The 100 that the couple met and fell in love – as did their characters.
Bob and Eliza wed on May 5, 2019, announcing they had tied the knot a month later much to the delight of their fans.
"I am so very proud of my husband, his courage, his vulnerability, and his determination... (I won the life lottery with this man!)" Eliza wrote on Instagram weeks after their wedding.
"So... as he would put it, so eloquently, as always - be well and be kind to one another - it's the most important thing in the world."
While the couple prepare to welcome their first child together, Bob has also been busy acting on Aussie screens in the BINGE Original Series Love Me. The romantic miniseries also stars Hugo Weaving and Bojana Novakovic.
If you're not already signed up to BINGE, you’re going to want to click here for a free 14-day trial to check out Bob in the series.
This article previously appeared on our sister site Now To Love.