This paper is a case study aiming to exemplify how long-term diglossic contact between closely related languages can affect linguistic structure. After a brief socio-historical overview focusing on the shifting role and prestige of Valencian and Spanish over the centuries, a selection of phonological, lexical, phraseological, discourse pragmatic and morphosyntactic features are presented and analysed in order to determine whether structural convergence has taken place between these two Ibero-Romance varieties. Apart from the expected use of lexical loans and frequent instances of code switching between the two languages by bilingual speakers, it is shown that the influence of Spanish on colloquial spoken Valencian has affected its linguistic structure in a variety of ways. This includes contact-induced features taken from Spanish, but also contact-induced conservation of older features that have disappeared from other varieties of Catalan. Particular attention is paid to innovations in spoken Valencian that are based on a combination of Catalan and Spanish structural features, sometimes leading to a reduction of structural complexity or opacity.