Who said "Gratitude is the mark of a noble heart."?

This quote is attributed to Rhaegar Targaryen.

Gratitude is the mark of a noble heart. - Rhaegar Targaryen

"Gratitude is the mark of a noble heart."

Rhaegar Targaryen Gratitude

"The dragon has three heads."

"I have a duty to my realm and to the future."

"Music is the voice of the soul."

"Love is the most powerful force in the world."

"Gratitude makes life richer."

"A grateful heart is a happy heart."

"Respect those who came before us."

"Life's greatest treasures are the people we love"