Rapunzel's Crown

The tiara of the Lost Princess is what got Rapunzel to leave her Tower and Flynn Rider.

Tangled
The crown is first seen being given to Corona's new born princess by the King of Corona and when she 'went missing' it became a reminder of her to the Kingdom and it's King and Queen. Keeping it safe until their princess returns home.

Eighteen years later it was stolen by Flynn Rider and The Stabbington Brothers for it's gold and diamond value and Flynn took it for himself while he and the brothers were getting away from the guards. When he lost them the thief found a hidden tower to hide in until the guards and the crazy white horse were gone, but he ended up being hit by a frying pan.

After the girl in the tower, Rapunzel realized that she can take care of herself she found the stolen crown in the 'man's' satchel, she hasn't seen a crown before and it took awhile to find where it is suppose to go; on her head. When Rapunzel failed to get "mother" to say "yes you can leave and see the flowing lights in person" again, she made a deal with the thief. She'll give him back his "satchel" if he takes her to lanterns and brings her back home unharmed. Not long after they left, Gothel came back to the tower to find her "flower" missing, the crown and a Wanted Poster of the thief.

Gothel later uses it to get the Stabbington Brothers to help her get Rapunzel back and get rid of Flynn; and she uses it again on Rapunzel as she made her believe that Flynn only cares about the crown's jewels and not her. The next night when Rapunzel's dream of seeing the flowing lanterns in person finally came true and was about to sent her own up with Flynn/Eugene, she gave the tiara back to him, but Eugene put it aside. The crown's value no longer means anything to him; only she matters.

The crown was later brought back to the palace by an unconscious Flynn tied to a small ship's helm, while back at the tower Rapunzel was having flack backs of her birth family, seeing a picture of her infant self and seeing herself as a princess in the mirror while wearing the crown; she realized that the crown was hers and that she was the Lost Princess. Later it was placed back on her head after Flynn had escaped, saved and brought her back home to her real/birth family. But from time to time Eugene still uses his thieving 'Rider' skills on it to tease Princess Rapunzel.

Tangled Ever After
Rapunzel wears the crown with her wedding dress as she and Eugene were be coming husband and wife: and the diamonds on her wedding resemble the tear shade diamonds on the crown.

Sofia the First
Rapunzel is seen wearing her diamond tiara in "The Curse of Princess Ivy", when Sofia's amulet called her to Sofia and Ambers' aid.