The story
- Englishgoing
- Englishto
- Englishgonna
- Proto-Indo-European*bʰuH-
- Proto-Indo-European*bʰuHyétider.?
- Proto-Germanic*beuną
- Proto-West Germanic*beun
- Old Englishbēon
- Middle Englishbeen
- Englishbe
- Englishwannabeinflu.
- English todaygonnabe
From gonna (“contraction of going to”) + be, modelled after wannabe.
Etymology from Wiktionary, CC BY-SA 4.0.