I never heard this song before I heard Peter, Paul, and Mary‘s wonderful version.
We would call this a Lament, would we naught?

POLLY VON
Peter, Paul, and Mary version, on their 1963 third studio album, In the Wind

In The Wind: Peter, Paul and Mary: Amazon.ca: Music

(more commonly found as “Polly Vaughn,” “Polly Vaughan,” “Molly Bawn,” or “Molly Ban”) is a traditional Irish/English folk ballad
— a tragic story about a hunter who accidentally kills his beloved after mistaking her for a swan.

🕯️ Core meaning

The song is a misfortune ballad: a man goes out hunting, sees something white in the bushes, fires, and discovers he has killed his love, Polly.
In many versions, she had taken shelter from the rain and was wearing a white apron, which led to the fatal mistake.
The emotional center of the song is guilt, grief, and the irreversible consequences of a moment’s error.

🌿 Origins and variations

Irish roots: The name often corresponds to Mailí Bhán (“Fair Mary”), reinforcing the imagery of whiteness and purity.
Printed history: No versions are known before 1806, though some may date back to the late 18th century.
Celtic myth connections: Scholars have linked the ballad to legends of swan maidens, women who transform into swans — a recurring motif in Celtic folklore.
Ghostly visitation: In many versions, Polly’s ghost appears before the trial to confirm the hunter’s innocence. In others, the supernatural element is absent.

POLLY VON Lyrics
as Interpreted by: Noel Paul Stookey / Peter Yarrow / Mary Allin Travers
I shall tell of a hunter whose life was undoneBy the cruel hand of evil, at the setting of the sunHis arrow was loosed and it flew through the darkAnd his true love was slain as the shaft found its mark
She’d her apron wrapped about her, and he took her for a swanAnd it’s, oh, and alas it was she, Polly Von
He ran up beside her and found it was sheHe turned away his head for he could not bear to seeHe lifted her up and found she was deadA fountain of tears for his true love, he shed
She’d her apron wrapped about her, and he took her for a swanAnd it’s, oh, and alas it was she, Polly Von
He bore her away to his home by the seaCryin’, “Father, oh, father, I murdered poor PollyI’ve killed my fair love in the flower of her lifeAnd I always intended that she be my wife”
“But she’d her apron wrapped about her, and I took her for a swanAnd it’s oh, and alas it was she, Polly Von”
He roamed near the place where his true love was slainHe wept bitter tears, but his cries were all in vainAs he looked on the lake, a swan glided byAnd the sun slowly sank in the gray of the sky

She’d her apron wrapped about her, and he took her for a swanAnd it’s, oh, and alas it was she, Polly Von

Second Hand Songs lists 63 recorded versions.
https://secondhandsongs.com/work/238215/versions