Ten years after announcing they were going to stop touring and recording as a group, the girls are back together on Michelle Williams's new track, "Say Yes."
"I am so excited. It's one of my favorite songs on my album, and it's with my sisters," Williams tells PEOPLE. "And I can't believe it's been 15 years [since we've met]. That's why I was so happy when they did my album and Beyoncé had her braids! It took me back when I first met her and she had those blonde braids. I was like, 'Oh my God, you're taking me back to 'Say My Name'!"
Williams says even though they're no longer constantly together, they have remained close and always show up for the major moments – including Kelly Rowland's recent nuptials.
"We're honored to be there for each other in our happy moments. I've never really had genuine female relationships until I met them," she says. "I don't care what anyone says, we miss each other. We have that spiritual bond with each other where we know when you're really tired, you need your sister with you today or you just need a phone call to let them know you're thinking about them. I call them my soulmates."
And while the singer is aware that she's been the target of online detractors – there are entire sites devoted to dissing her – she says she lets the haters be her motivators.
"They are crazy! They're someone who take time to Google me daily and dedicate their website to me. I try to ignore it. I've been able to say, 'Okay, my name is in your mouth. You're searching for me on Twitter. I don't even know you exist.' "
And while Rowland and Beyoncé are seemingly the most visible of the trio, Williams, who is currently filming the Oxygen TV show Fix My Choir, says she continues to work nonstop.
"A lot of things I do go under the radar, so people do feel that I'm not as successful as the other ones, but I've made Broadway history and my fourth album is coming out. I've been working 15 years straight. I haven't stopped."