Christina Aguilera and Pink's relationship started off on an icy note when the initial talks for a cover of LaBelle's "Lady Marmalade" sung by Christina, Pink, Lil' Kim and Mya for the Moulin Rouge! soundtrack started. Pink recalled the first conversation about the superstar collaboration where Aguilera reportedly walked in with label executive, Ron Fair, in her Behind the Music segment on VH1:

"Ron Fair walked in. He didn't say hi to any of us and said, 'What's the high part? What's the most singing part? Christina's going to take that part.' And I stood up, and I said 'Hi. How are you? So nice of you to introduce yourself. I'm Pink. She will not be taking that part. I think that's what the fucking meeting's about.'"

Watch her explain it at the beginning of the video above.

Rockiness factor: Tiny earthquake.

On the surface, it seemed like everyone got along during the heavy promotions for "Lady Marmalade." The foursome performed at huge events like the 2001 MTV Movie Awards and the 2002 GRAMMYs, while the song hit No. 1 on the Billboard Hot 100, and won them Video of the Year at the VMAs and a GRAMMY Award for Best Pop Collaboration with Vocals. Throughout it all, Pink and Xtina (along with Kim and Mya) hugged each other and appeared on red carpets together.

Rockiness factor: Prairie-land flat.

In 2001, Pink reinvented herself with a more raw, rock-pop image on her Missundasztood album, in large part thanks to production work from 4 Non Blondes singer Linda Perry. Christina said she was inspired by Perry's songs on the record and reached out to work with the producer, resulting in songs like "Beautiful" and "I'm Ok," which detailed Christina's experiences with domestic abuse as a child.

Watch above at the 3:00 mark where Pink all-but-confirms she wasn't happy Linda was working with Xtina:

"I took it really personally when she started working with other artists, particularly artists I didn't like. I don't think imitation is the highest form of flattery. I think it's annoying." 

Rockiness factor: 7.0 earthquake with multiple aftershocks.

During her 2004 tour for third album Try This, Pink performed "Lady Marmalade" and it included a routine with blow-up dolls that people mentioned looked like Xtina. Pink more or less confirmed she was poking fun at Christina when she sang a line of "Beautiful" to the blonde doll once (see above at 1:40).

The news came after there were rumors Pink originally wanted "Beautiful" for her Missundasztood album and Linda wouldn't give up the song, only to later give it up to Christina for Stripped.

Rockiness factor: Grand canyon-esque.

Fast-forward to 2010 and it appears all the bad blood had been forgotten with Pink taking to Twitter to praise "You Lost Me," the second single off Christina's Bionic album.

Rockiness factor: That of a puddle after a long rain storm.

The awkwardness was palpable when Ryan Seacrest connected in Pink's phone interview when he was finishing up with Christina Aguilera, forcing the rivals to come voice-to-voice on the phone. Xtina does her best to wish congratulations to a then-pregnant Pink, adding that they should have play dates with their kids, to which Pink answers with a "ha ha" which anyone could read as a flat-out "No."

Listen to the audio above.

Rockiness factor: Gravel-like, but the really annoying gravel that shakes your car.

When news came out that Xtina and her boyfriend Matthew Rutler were arrested for public intoxication (where no charges were officially charged), Pink commented on the matter on Twitter showing that out of the early-'00s divas Britney Spears, Christina and herself, the edgy singer ended up being the only one not to ever be arrested. 

Rockiness factor: Like tripping on a rock after you already tripped and your glasses broke.

While the ladies have more or less stayed clear of one another, but Christina's name popped into Pink's during a concert 2013 Australian concert. She was performing "The Great Escape" before adding a bit of unexpected rasp into a note, quickly saying "I sounded like Christina Aguilera for a second, sorry!" and cracking herself up.

Watch it happen at :13 seconds in above.

Rockiness factor: Choppy waves.

The divas reunite onscreen the week of May 16, 2016 as Pink was named an advisor to the Top 8 contestants on The Voice Season 10. In the episode pieces we saw everything seems fine—though, some speculate Christina's "Bite Me" shirt might be more than just a cute saying. Also, at one point, Pink remarked "My hands are sweating, I feel uncomfortable" when sitting alongside Xtina, though it was actually in reference to how good the contestants were performing. Viewers noted that both women seemingly wanted to make for good TV and get along, careful not to step on each other's toes. But what Pink said after the taping, gives us hope (see next slide).

Rockiness factor: Slightly unpaved stretch of highway.

After 15 years of rockiness, it seems like Pink and Christina are finally, really friends. When Entertainment Tonight asked her who she had the most fun with on set of The Voice, Pink gave the unexpected answer of her longtime frenemy:

"Her and I have had history and it hasn't always been wonderful, but finally, I think it just took us 15 years, and I feel like there was true love. It felt really good. I love when you're around to have a full-circle moment and that was a full-circle moment for me because—in all honesty—I'm a fan of hers."

Awww! So is this feud officially over? See an update on the next slide!

Rockiness factor: An undisturbed pond of crystal-clear water.

On August 16, 2017, when MTV announced Pink will receive the 2017 VMAs Video Vanguard Award, social media was, expectedly, a hotbed of both hate and love. Many music fans were excited and happy for Pink, but a few Christina fans felt their fave deserved the award first. Some fans even sent immature or nasty tweets in Pink's direction. How'd she respond?

In true Pink fashion, she called out the haters, but decidedly turned a negative into a positive, quote-replying to an Xtina fan the above tweet. "Want to point out an awful new phenomenon of the last 10 years. We can no longer be happy for each other. I (heart) Xtina, we've made amends...."

So, what's next for this duo of kick-ass, mature women with big voices and illustrious legacies? We'll just have to wait and see...

Rockiness factor: A perfectly smooth, polished marble countertop.