Heart Of The Ocean

The Heart of the Ocean (also known as Le Cœur de la Mer) is the name of a fictional blue diamond featured prominently in the 1997 film Titanic.

Hero: The Guardian Smurf stories
At an early point in the series, Hero, with the help of Miner and Handy created a necklace with a diamond chain, with a heart-shaped amulet attached to it containing a rare blue diamond to present to Wonder as her birthday present. But due to its beauty, it caused a lot of arguments amongst the Smurfettes as to who would wear it. So it was hidden away in a secret location known only to Hero. It wasn't until later in the future when Hero had married Smurfette, that he gave it to her as a Christmas present.

Trivia

 * The picture of the Heart of the Ocean used in the article is taken from Google.