This study is concerned with finding out how L3 (third language) learners recognize and make conscious use of cross-linguistic similarities and differences and whether their metalinguistic reflections are in correlation with their proficiency. Written text productions of thirteen L3 learners of English, aged 20-25, at different L3 levels (A2, B1, B2 and C1) with various L1s and a constant variable of L2 German acquired before their L3 were used as prompts for subsequent individual reflection sessions. The retrospective data gave insights into L3 learners' thought processes contributing significantly to the limited number of studies. The results showed that: (a) metalinguistic knowledge about one language did not result in reported activation of that language, (b) self-repair was not correlated with proficiency, (c) there is a link between explicit deficit statements, intuitive statements, over-monitoring, metasyntactic and metaphonological awareness, and their occurrence at B2 level. Finally, the metalinguistic reflection ability was demonstrated to involve an interaction of metalinguistic awareness, cross-linguistic awareness, metalinguistic knowledge, self-repair, detection of violations and analysis of linguistic features. [This paper was presented at the 13th International Conference of the Association for Language Awareness, Vienna, July 2016.]