Tangled

Long ago, a drop of sunlight became a golden flower capable of healing illness, decay and injury. For hundreds of years the flower is used by Mother Gothel to retain her youth until it is discovered by soldiers of a nearby kingdom, Corona. They use the flower to heal their ailing queen, who soon afterwards gives birth to Princess Rapunzel. While attempting to recover the flower, Gothel discovers that Rapunzel's hair has the flower's healing properties. However, attempting to take just the hair by cutting a piece from it destroys its power, and so she kidnaps Rapunzel and raises her as her own daughter in an isolated tower. Once a year, the King and Queen release sky lanterns on Rapunzel's birthday, hoping for their daughter's return.
Nearing her eighteenth birthday, Rapunzel asks Gothel for permission to leave the tower and discover the source of the lanterns, but Gothel refuses, telling her that the outside world is a dangerous place. Elsewhere, a thief known as Flynn Rider has stolen Rapunzel's crown from the kingdom and inadvertently discovers the tower after ditching his cohorts, the Stabbington brothers. Rapunzel captures Flynn and discovers the crown, but is unaware of its significance. Rapunzel plans to show Flynn to Gothel in order to prove she can take care of herself, but when Gothel becomes enraged at Rapunzel's insistent desire to leave, she asks for a special paint that will take Gothel three days' round trip to obtain and return. Gothel agrees and departs. Rapunzel convinces Flynn to escort her to see the lanterns in exchange for the crown.
During their excursion, Flynn takes Rapunzel to the Snuggly Duckling, a pub filled with the frightening people Gothel warned Rapunzel about, but who instead are charmed by Rapunzel's innocence. When the royal soldiers appear searching for Flynn, the pub regulars help the pair escape. The soldiers give chase, led by Maximus, one of the lead horses in the royal army, and locate them at a dam. The dam is inadvertently breached, and the resulting deluge traps Flynn and Rapunzel in a flooding cave. Fearing this is the end, Flynn reveals his real name is Eugene Fitzherbert. Rapunzel starts to reveal that her hair glows when she sings â but then realizes that this is their key to escape, as her hair provides enough light to find a way out of the cave. Eugene and Rapunzel take refuge in a forest where Gothel, now in league with the Stabbingtons, gives the crown to Rapunzel and suggests using it to challenge Eugene's interest in her.
The next morning, Maximus finds the pair and tries to capture Eugene, but Rapunzel arranges a truce in honor of her birthday. The group reaches the kingdom and enjoys the festivities, culminating in an evening cruise as the lanterns are released. There, Rapunzel gives Eugene the crown. When he sees the Stabbingtons on the shore, Eugene leaves Rapunzel and intends to let them have the crown. Instead, the brothers tie Eugene onto a boat and confront Rapunzel, claiming Eugene is escaping with the crown. Gothel then stages a rescue by betraying the brothers and returns Rapunzel to the tower as Eugene and the Stabbingtons are arrested by the royal guards.
Back at the tower, Rapunzel recognizes the symbol of the kingdom, which she had subconsciously incorporated into her paintings over the years. Realizing that she is the long-lost princess, she confronts Gothel. As Eugene is being led to execution, he is rescued by the Snuggly Duckling regulars and carried back to Gothel's tower by Maximus. Eugene enters the tower by climbing Rapunzel's hair, only to find Rapunzel bound with chains and gagged with a handkerchief. Gothel then stabs him with a knife and attempts to leave with a struggling Rapunzel. Rapunzel agrees to lifelong captivity if she is allowed to heal Eugene, but before she has the chance to save him, Eugene slices off her hair, turning it from golden blonde to brown and destroying its magic. Gothel's age rapidly catches up to her, and she falls from the tower, disintegrating into dust. As Eugene dies, a heartbroken Rapunzel's tear, which still contains a bit of the sun's power, lands on his cheek and restores his life. The two return to the kingdom, where Rapunzel is re-united with her parents. The kingdom breaks out in celebration, and Eugene is pardoned for his crimes. Rapunzel and Eugene eventually marry.

Question: Who discovers that Rapunzel's hair has healing properties?
Answer: Gothel.