Sarah Jane Nader Joining 'Dancing with the Stars,' Paired with Female Pro

Sarah Jane Nader's pirouetting into the new season of "Dancing with the Stars" just like Brooks did a couple of years ago ... but there's one big difference ... sources tell us Sarah is paired up with a female pro.

The brunette bombshell was spotted leaving the 'DWTS' dance studio Thursday in a low-cut black athletic top and form-fitting sweats ... keeping a low profile with an opaque facial covering obscuring her features, while making sure to show plenty of cleavage.

Other big-name contestants include Jenna Dewan, Tatyana Ali, Tyler Cameron and Jimmy Kimmel's sidekick Guillermo.

Sarah isn't the only person with a family connection to a past contestant either ... because Whitney Leavitt's husband -- Connor -- has also quickstepped his way onto the show while his better half continues to tear it up on Broadway.

Worth noting ... Brooks didn't win her season of 'DWTS' -- but she did enter into a temporary fling with Gleb Savchenko, which didn't end well for anyone.

While Brooks is over in Europe going topless for the cameras, Sarah is hard at work ... and being slightly more modest when it comes to boobs.

We're sure Brooks counseled her sis against entering into a showmance ... but blood runs hot in the ballroom.