بسم الله الرحمن الرحيم
(Fatwa: 1493/1493/M=12/1434)
Ghusl becomes wajib due to ihtilam (wet dream). Thus, in this case the Fajr Salah you performed was not valid. It is compulsory to do full ghusl and perform salah again.
Allah knows Best!
Darul Ifta,
Darul Uloom Deoband
