If you’re anything like us, some of your favorite memories include bundling up with your pet and blanket to watch The Powerpuff Girls. Tuning in to the adventures of Bubbles, Blossom, and Buttercup was both comforting and inspiring, reminding us that a little sugar and spice does make everything nice. We still love seeing the trio save the world, and now we may have more to love because The Powerpuff Girls are officially getting another member. The only downside is we don’t know who this mystery member is…yet.

To find that out, we’ll have to change the channel to Cartoon Network on September 17th.

According to Entertainment Weekly, the reveal will take place on Sunday, September 17th at 5:30 p.m. ET during The Powerpuff Girls: Power of Four. This is the first installment of a five-part movie event, so we imagine that there will be plenty of crime-fighting and world-saving going on, and maybe a little bit of drama, too. After all, we don’t know how or why this new mysterious Powerpuff Girl came to be.

Of course, the internet has major feelings about this. Some are excited that they’ve been around long enough to see this happen. I mean, it does feel like an accomplishment when you realize that this show originally aired in the late ’90s.

People even have theories about who this new Powerpuff Girl could be. The most notable possibility is Bunny, a fourth Powerpuff Girl who the trio made to help them fight crime. She was only in one episode, “Twisted Sister” in Season 2, and she was wearing a purple outfit that matched the trio’s.

Since the reveal of a fourth Powerpuff Girl is in shades of purple, well, let’s just say we also have our suspicions.

While we’re not sure if this is the real mystery sister, we’re still excited to see if our prediction is true. After all, who says The Powerpuff Girls all have to be girls anyway? We’ll just have to tune in on September 17th to find out.