The pair - who revealed their baby news earlier this month - made a picture perfect couple as they attended an event at Sky Beach, The Tropicana, LA, that was marking the national U.S holiday.
Showing off a little baby bump, Blac was gorgeous in a thigh-skimming white halter neck dress, which gave us a glimpse of her impressive tattoos. Teaming the frock with laced-up heels and neon orange talons, she looked as hot as ever - no reaching for the tracksuit bottoms for this mum-to-be!
Meanwhile, Rob kept it pretty casual for the occasion, opting for black shorts and a polo t-shirt, which he wore with trainers and a blue baseball cap.
Rob and Blac took to Instagram a few weeks ago to announce that they were expecting their first baby together. They first started dating at the beginning of this year and went on to get engaged when Rob, 29, popped the question to the American model.
For Rob, it's the first time he'll be a parent, while Blac, 28, is already a mum to King Cairo, three, who she had with ex Tyga (who is also Kylie Jenner's ex!).
Earlier this week, a very happy Blac couldn't resist taking to social media to share a scan photo of their unborn child and wrote a gushing message about the pregnancy, saying:
"For a long time I felt like King was going to be an only child. That he was my greatest blessing and we were gonna live happily ever after together, just the two of us, I was no longer looking for love because I thought I had all that I needed. We needed.
"But look at God ! Here I am engaged to be married to one of the greatest men I know who loves King & I unconditionally AND having another bundle of joy! I just want to say Never give up & ALWAYS have faith because fairytales DO come True.