Brian Grazer is going to marry his girlfriend of five years, Vietnamese concert pianist Chau-Giang Thi Nguyen. The spiky-haired, Oscar-winning producer, who founded Imagine Entertainment with Ron Howard in 1986 and has been behind movies including “Apollo 13,” “A Beautiful Mind” and “The Da Vinci Code” and the hit series “24,” confirmed to Page Six yesterday that the pair are engaged. Nguyen told us, “We are both really, really happy. On Sept. 18, we will have been together for five years. We are not sure of the wedding date, but it will be in LA sometime around the fall.” She’s sporting a diamond ring and said her dress will likely be Valentino, who “often dresses me for my concerts.” She added, “I will be writing a lot of music for my wedding. It is going to be very special.” Grazer has a few other big productions in the works. The big-screen version of “24” is set for 2012, while he and Howard are casting the “Dark Tower” movie and TV adaptation of Stephen King‘s novel.