Hoax mastermind Ronaiah Tuiasosopo’s pretty young cousin played the part of “Lennay Kekua,” the fake girlfriend he created, The Post has learned.

Tino Tuiasosopo convinced the Notre Dame grid star that she was the real deal, calling him at school, telling him she loved him and even sobbing hysterically when another girl answered his phone, several of the woman’s relatives said yesterday.

“Tino is the girl that Manti has been talking to all these months,” said a Tuiasosopo cousin.

The revelation shoots down claims by Ronaiah Tuiasosopo’s attorney, Milton Grimes, that Ronaiah altered his masculine voice to play the part of the chirpy, flirty Kekua.