In one well-known version of the legend, a young man named Maelon Dafodrill falls in love with Dwynwen, but she rejects him;[4] in another, she cannot marry him because her father has already promised her to another.

As a mark of thanks, she retreats to the solitude of Ynys Llanddwyn off Anglesey, becoming a hermit until her death around AD 460 (some texts say she fled there out of fear of Maelgwn Gwynedd).

[3] A holy well on the island, associated with Dwynwen, became a site of pilgrimage, where the movements of sacred fish within its waters were thought to forecast lovers' fortunes.

Pilgrims looking for a holy site increasingly turned to Saint Elian's Well nearby, though some continued to honour Dwynwen at her ruined church.

[18] During the 1960s, a Bangor University student, Vera Williams, sought to revive St Dwynwen's Day by designing Welsh \"Valentine's\" cards.

[8] St Dwynwen's Day celebrations have grown in popularity, with events like concerts, parties, and the exchange of greeting cards becoming increasingly common.

A major boost came in 2003 when the Welsh Language Board partnered with the supermarket Tesco to distribute 50,000 free St Dwynwen's Day cards across Wales.

[20] The board also encouraged alternative celebrations, such as hosting love-themed gigs, singles nights, romantic dinners, or composing love poetry in pubs.