Taylor Swift and Selena Gomez have taken on a new celebrity friend. Tuesday night, the BFFs threw a birthday party for Camila Cabello of Fifth Harmony.

As Mila rang in the big 1-8, Swift ushered in her gaggle of besties, including the Haim sisters, Hailee Steinfeld, Sarah Hyland, Hayley Williams and Jaime King (Tay just became godmother to Jaime's next kid).

Both Swift and Gomez posted pictures of the star-studded birthday party. And while they celebrated, so did Camila's fans -- called Harmonizers. Fans and bandmates alike posted cute notes online for the singer. Here's what her Fifth Harmony pals said on Instagram:

Normani Kordei

"HAPPY BIRTHDAY to my lil baddie MÍRA I can't believe you've finally approached adult hood you grown women you . I remember being at boot camp the girls and I having to teach you how to walk in heels and you totally just eating the floor multiples times but you've completely transformed before my eyes into such a beautiful , strong , intelligent women not completely graceful but definitely inspiring to not only to me and the girls but to many of other people in this world . you have such a powerful impact and voice ❤️ you're such an amazing heart and I'm so grateful that we are able to exist at the same time . you have taught me many things and showered me with nothing but wisdom and comfort when in need . I'm so proud of you and I'm thankful that we're able to watch each other grow . YOU'RE LEGAL meaning you get to twerk 50% harder lmao I love you mama #HAPPYBIRTHDAYMÍRACABELLO - moaney"

Ally Brooke Hernandez

"#HAPPYBIRTHDAYCAMILA MY MIILAAAAA!!!! Woah what the heck. Is it really here?! Are you really the big 18?!!? OMG!!!! Finally girly!!! I just want to say that it's been so awesome seeing you grow over the past few years. You've grown into a beautiful, confident, brave young woman and I am so grateful for the laughs we have been able to share together. I WUV you so so much and hope this bday is wonderful. 18 is a pretty great age so ENJOY IT!! YOU'RE LEGAAALLLL NOW YAY!! Muah muah MUAH God bless you girly"

Lauren Jauregui

"Super cute candids taken by a random stranger always make good birthday post pics. HAPPY 18TH BIRTHDAY CAMILA CABELLO. YOU'RE LEGAL NOW YAYYY!!!!!! You are such a beautiful person inside and out and I'm so thankful that I get to call you my friend. Thanks for all the laughs, for being my shoulder to cry on whenever I've needed a friend, for giving amazing sound advice (even though you're just now considered an adult by the government you've been there mentally for a while which I greatly appreciate) I wish you many more years of amazingness and I hope you had the best day with your family. You deserve all the love and happiness the world has to offer and I wish it all upon you for many many years to come. I LOVE YOU CAMZZZZ"

Dinah Jane Hansen

"Somewhere in the world it's still March 3! And I know I'm a little late bt I promise WALZ I didn't forget how SPECIAL this day is! So let me start off by saying how THANKFUL I am to have you in my life! The sleepless loooonng nights we stay up talking about 'LIFE' aka boys ... the many 'missions' we stay pullin behind Big Robs back (jk big Rob if your reading this hehe) the many DRY jokes we tell each other .. And PRETend like it was the funniest thing ever lol the many many nick names we have for each other .. (Why do we do this btw? Lol) The times we 'WINGMAN' for each other wink wink and the times we share secrets and know that We can TRUST each other .. the dance parties we have in our hotel rooms and even tho I'm not feelin your playlist sometimes . . I ain't gotta choice bt slowly love ur music! Lol the many times we have cried and wiped each other's tears !! I THANK GOD for you! You are one of my BESTess friends my lifetime sister my everything .. HAPPY BIRTHDAY OLD HEAD.. Your an adult now ewww lol jk jk I pray you have many more years to come WALZ! 'Love always CHEENS'"

Ps: just so you all know I willingly let her CAKE me in the face