Zac Efron, Vanessa Hudgens' romance was 'so high school,' says 'HSM' cast

Zac Efron and Vanessa Hudgens may have lost touch with each other over the years, but they were once considered the ultimate Disney Channel couple during their High School Musical era.

A new book, Disney High: The Untold Story of the Rise and Fall of Disney Channel's Tween Empire by culture journalist Ashley Spencer, offers fresh details on how the young couple’s relationship truly unfolded in the most “high school” way.

According to Lucas Grabeel, who played Ryan Evans in HSM, the sparks between the two began early. Casting director Natalie Hart recalled Hudgens being nervous for her audition opposite Efron, calling him "too cute," but their chemistry was undeniable.

“It was magic,” Hart recalled of the pair’s first scene together.

Once cast as Gabriella and Troy, Hudgens quickly fell “head over heels” for Efron, despite him having a girlfriend at the time.

Choreographer Chucky Klapow remembered a key moment when Efron opened up about his conflicted feelings, telling him, "I don't know what to do, man. Vanessa is super into me, and I have feelings for her, too.”

Efron didn’t want to do wrong by his then-girlfriend, but he also didn’t want to “shut Vanessa down and ruin the chemistry in the movie.”

Encouraged to follow his heart, Efron and Hudgens officially became a couple, leading to the start of their highly publicised relationship.

Grabeel recalled Hudgens being completely smitten with Efron, describing him as "the sun and moon to her."

However, their romance came with challenges, and after five years, the couple split in 2010.