Does anyone know how Radagon has the Elden Ring inside him during our fight?

You can clearly see the whole Elden Ring as we know from the box art in Radagons torso but shouldnt that be impossible? Marika shattered the Elden Ring and it split into the Great Runes, then the tarnished comes along and gathers the Great Runes to repair the Elden Ring so shouldnt we have the collective Elden Ring in our possession? Why does Radagon have it inside him? And hell, why does the Elden Beast even exist as a whole entity when its the living true from of the Elden Ring?

https://preview.redd.it/ni9wd4g262vc1.jpg?width=711&format=pjpg&auto=webp&s=7493ba0d87a338926b0397775f64360db00234d1