The 31-year-old was a popular figure at the Amex Stadium having helped Brighton win promotion to the Premier League in 2016-17 and in The Seagulls' first two seasons in the top-flight he was a regular starter. He made over 100 appearances during his time with Brighton and was their first-choice left-back during his first four years at the club.
Over the course of his career, Bong has played at the highest levels including the Premier League, French Ligue 1 and the Greek Super League and has also played in the group stages of the Champions League during his time with Olympiacos.
Bong has represented Cameroon 16 times at international level, including in the FIFA World Cup and in last year's African Cup of Nations and has also captained his country on a number of occasions.
The defender has now joined up with the Forest squad ahead of Saturday's trip to Birmingham City.