The 62-year-old shared a photo slideshow on social media on Thursday in honor of the theme.
The first pic featured a stunning throwback bikini photo, which shows the mother-of-one in a teeny-tiny hot pink two-piece posing on the beach in the 1990s.
“Queen of working out way back at 37 years old! #tbt Tune in tonight for an all new #RHONY and watch us get our aerobics on! @bravotv,” she wrote.
The second photo shows the reality TV star lifting weights in a silver sports bra and multicolored biker shorts. And the last pic is Singer posing with friend and fellow castmate, Dorinda Medley, in their brightly colored aerobic outfits from the episode.
Singer previously revealed that she keeps her enviable shape by working out at least twice a week.
She told Allure magazine in 2015, "My trainer focuses everything on the core. It's great; we'll do a kettlebell, now it's up to 30 pounds, and I swing it between my legs. And with a kettlebell that is maybe 15 pounds, I go down with a lunge, with my arms lifting up and down.
"And one really good one is when I'm on the Bosu ball. I take weights, with my arms out, and lunge down. It just makes you cut. It's a very intense hour of training. And I try to run, too, because if I want to stay really lean, I need to do things in between the workouts," she added.
Singer also said she loves to run, play tennis, and do yoga.