She hasn't given us all of her Glory just yet.

Britney Spears' ninth studio album has yet to be officially released in Japan. And when it does, it'll include one extra song in addition to the already sizable collection of 17 tracks that fans have been not-so-patiently awaiting: "Mood Ring," produced by DJ Mustard, which he's teased for well over a year now.

The song's co-writer, Melanie Fontana, who's also responsible for penning upcoming cuts for the likes of The Chainsmokers, Daya and John Dahlback, as well as Aaron Carter's forthcoming EP, recently spoke to PopCrush about the story behind the forthcoming track — described as a "favorite" by Britney's A&R, Karen — just before it arrives on September 14.

"My love is a mood ring / Up-and-down emotions, all these mood swings..."

"Mood Ring" was originally meant to be "Mood Swings."

"I wrote the song with my friend Jon [Asher], who is an amazing songwriter and one of my really good friends. I had an idea: I wanted to write a song called "Mood Swings." We started with some melodies and nothing really hit us. So we went down, started to hang out in his kitchen, had something to eat, and he was like 'Mood swings, mood swings...what about mood ring?" And I was like "Oh my God, 'Mood Ring'!" And that's kind of how it happened: basically joking around while we were having a snack in the kitchen. He came up with the title. We were thinking about it, in our minds, as The Chainsmokers featuring Britney Spears. So that was the concept and sound."

It was written with Britney's life in mind.

"We were writing it for Britney from the beginning. Whether or not it got cut by Britney, we were not sure at that moment, but we were writing it from the perspective. By the way, we're diehard fans — like childhood on, all the way on up. I think he and I both have a great channel for Britney, just because we're superfans. That's how the start was birthed. We love how Britney's gone through all her phases, and hair colors, and literally, like, mood swings. Her whole life is like a mood ring."

The acapella sat for three months — until Mustard jumped on the beat, hoe.

"We wrote it on a piano track. I sent the acapella to a couple of friends in Finland, to people in LA, on the East Coast...but nobody really cared. One of Jon and my really good friends is also friends with Mustard and that whole team. So he emailed the acapella for us to Mustard's camp. And within, like, two days of him sending the acapella out to Mustard, we had a scratch demo."

Then Mustard reached out to Brit.

"We knew the song was really, really special, but we didn't realize it until it was that quick of a turnaround. About a month after that, I got a phone call while I was working in Finland. I was writing in Helsinki, and I got a call that Britney was recording it. I literally almost bought a ticket home. I was on American Airlines trying to buy a ticket home. They were like 'No, don't, it's fine! It's going to be a two hour session and won't be a big deal!' I was like 'Are you sure?! I'll come home now!" [Laughs] Mustard delivered it to Britney. I wish that I had some sort of part of that, but it had nothing to do with me at all. Our sound was just so perfect for her — it was a no brainer when he gave it to Larry Rudolph."

And Britney loved it.

"We were told by the head of A&R, Karen Kwak, that it was her favorite song, initially. It was her favorite song. Over and over again, this is what we kept hearing. She felt the most connected to it of all the songs, which is why we were so surprised when we found out it was just on the Japanese edition."

The song is only available in Japan, for now...

"At first, I won't lie, I was upset — it's being banished to Japan! But I do a lot of work and writing in Japan and Korea, so I know records still actually sell over there. It's smart, knowing physical copies will fly off the shelves over there. [Glory] will probably be No. 1 in Japan on the 14th. They're being wise. You have to buy the whole album. They're just being smart about it."

...And there's always a chance it could head stateside, too.

"Mustard is working on his project very heavily right now. Would it shock me if it came out? I would not be surprised if it came out as a single. I feel like it could be."

They've got more (moah) songs lined up for her when she's ready to record again.

"We wrote probably, like, ten more songs that could have gone on her album. Me, Jon Asher and I — we could bring back 2001 Britney today if that's what they wanted. We have ten other "Mood Ring"-s in the holster. But her album was already so politically tied up that, basically, there some blockade with management. She wasn't able to cut the songs. Our goal for Number 10 is that we get 10-for-10 on her 10th album. I want to Executive Produce the whole thing. I know that sounds a little delusional. [Laughs]"

"Mood Ring" will arrive on September 14. Listen to a preview on HMV Japan.

Check out the lyrics to "Mood Ring" below, courtesy of co-writer, Jon Asher:

Britney Spears Through the Years: