There flying Elwing came to him,
and flame was in the darkness lit;
more bright than light of diamond
the fire on her carcanet.

The Silmaril she bound on him
and crowned him with the living light,
and dauntless then with burning brow
he turned his prow; and in the night
from otherworld beyond the Sea
there strong and free a storm arose,
a wind of power in Tarmenel;
by paths that seldom mortal goes
his boat it bore with biting breath
as might of death across the grey
and long forsaken seas distressed;
from east to west he passed away.

(...)

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piece of Bilbo's song in Rivendell
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JRR Tolkien, The Lord of the Rings
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Elwing brought the silmaril to Earendil and married him.

Earendil became the evening star (remember what Galadriel told Frodo about that shiny glass she gave him?...) He flies an enchanted ship, bringing light to Arda.

his wife Elwing developed the ability to became a sea gull...

This drawing shows Elwing coming back to her elf form

hope you like!