The song is about his first girlfriend, the titular Gwendolyne, a French girl whom he met at the age of twenty while still a law student and a goalkeeper for Spanish football team Real Madrid Castilla.

In 1963, Iglesias was involved in a near-fatal car accident, which ended his football career, left him in rehabilitation for considerable time and indirectly led him to start learning the guitar, as a means of physical therapy.

[3][4] He released "Gwendolyne" in five languages: Spanish, English –with lyrics by Marcel Stellman–, French, German, and Italian,[5] and toured several European television stations promoting the song.

[6] On 21 March 1970, the Eurovision Song Contest was held at the RAI Congrescentrum in Amsterdam hosted by Nederlandse Omroep Stichting (NOS), and broadcast live throughout the continent.

Iglesias performed "Gwendolyne" ninth on the evening following Luxembourg's "Je suis tombé du ciel" by David Alexandre Winter and preceding Monaco's "Marlène" by Dominique Dussault.

[10] At the close of voting, the song had received eight points, placing fourth in a field of twelve, in a tie with "Marie-Blanche" by Guy Bonnet for France and "Retour" by Henri Dès for Switzerland.

[13] On 28 June 1970, TVE aired a special musical show filmed at the World Exposition 1970 in Osaka, directed by Valerio Lazarov and featuring Massiel, Karina, Julio Iglesias, and Miguel Ríos.