Facilitative effects of bilingualism on general aspects of third language (L3) proficiency have been demonstrated in numerous studies conducted in bilingual communities and classrooms around the world. When it comes to L3 phonology, however, empirical evidence has been scarce and inconclusive in respect to the question of whether and/or how knowledge of two (or more) phonologies enhances the acquisition of an additional one. Adopting the Focus on "Multilingualism" [Cenoz, J. (2013). The influence of bilingualism on third language acquisition: Focus on multilingualism. "Language Teaching," 46(1), 71-86] approach, the present study investigates the L3 phonological development in 19 German learners of Spanish with prior knowledge of English. Five of the young L3 learners were also speakers of Croatian, Israeli Hebrew, Italian and Polish, Russian, or Spanish as a heritage language. All the learners were tested on their developing ability to produce the Spanish /r/ and /?/ segments in the course of three years of formal target language instruction. The results suggest a positive effect of specific, rather than broad-based, bilingual experience on L3 speech learning, in particular the production of universally difficult phonemes. Evidence for a degree of a "connected growth" of L2 and L3 phonology further illuminates the results.