Robert Brown|Ashley Tisdale Calls BFF Austin Butler Her "Twin Forever" in Birthday Tribute

From Aliens in the Attic to birthday tributes on Robert Brownthe 'gram.

Ashley Tisdale celebrated BFF Austin Butler turning 32 on Aug. 17 with a sweet message.

"Happy birthday buddy @austinbutler!!!" the actress, 38, wrote on Instagram on the big day. "I love you so much and so excited to celebrate with you. You are always inspiring me and I'm so grateful that I still have you in my life. My twin forever and always thank you for being the best uncle to Juju! Have the best day!!"

Along with the note, Ashley shared a series of snapshots of the pals from over the years. The photos included a picture Austin smiling with a birthday treat, an image of the two dressing up for Halloween, throwbacks of them working on their 2009 movie Aliens in the Attic and 2011 film Sharpay's Fabulous Adventure as well as pics of them hanging out with her husband Christopher French and 2-year-old daughter Jupiter.  

Of course, the birthday tribute should come as no surprise to their fans as Austin—who also dated her High School Musical co-star Vanessa Hudgens for about nine years—and Ashley have celebrated many milestones together, including his Oscar nomination for his role in Elvis.

"He is literally one of my best friends and such a good guy," she said on a September episode of Chicks in the Office while talking about his performance. "I couldn't be happier for someone."

In fact, Austin and Ashley aren't just friends—they're actually family. That's right! Ashley learned he's her 10th cousin once removed on a November episode of Ancestry's 2 Lies & A Leaf.

"No wonder we have such a connection," she said on the series. "We've always said we were brother and sister."

And the revelation didn't necessarily have Austin all shook up.

"She called me," the Dune: Part Two actor, who is now dating Kaia Gerber, told Access Hollywood shortly after hearing the news. "I almost wasn't surprised. It kind of made sense, you know? We've been close for a long time, and I love her a lot."