Evan Agostini / Evan Agostini / AP

Whitney Houston in 2009.

In an upcoming interview with Anderson Cooper, Kevin Costner tells the talk-show host he twice wrote letters to his "Bodyguard" co-star Whitney Houston to try and encourage her to conquer her addictions.

“There are some people that really love Whitney, and a couple times during the last seven, eight years, (they) asked me, would I write her a letter?” recalls the actor, who spoke at the singer's February funeral. “She would always be close to me, she would always be somebody I appreciated.”

“When someone says, will you write a letter to someone who you know is having trouble … I did.” he adds. “I don’t know if those letters were ever read.”

Costner spoke to Cooper on the host's daytime talk show, “Anderson,” for an episode that will air in May. The actor is currently promoting his new mini-series, “Hatfields & McCoys,” which premieres on the History Channel on May 28.

Cooper asked Costner about the toxicology report on Houston, which revealed chronic and long-term usage of cocaine by the singer.

“Was she going through those struggles when she was doing 'The Bodyguard'?” Cooper asked Costner.

“Not that I know of, no,” he replied. “I elected to let Whitney have her life after 'The Bodyguard.'”

At Houston's funeral, Costner described the "Whitney that I knew” as someone who lacked self-confidence and always questioned her own abilities. He observed how such scrutiny both helped her to advance, and ultimately, led to her decline.

Costner told Cooper on his show, “I know I have this level of celebrity, of fame, international, national, whatever you want to call it, but it’s a pretty surreal thing to think sometimes that you’re in the middle of another famous person’s life and you think to yourself, ‘How the hell did I get famous? What is this some weird club that we’re in?’”

Costner also said that he had spoken to the the late Princess Diana about the possibility of her starring in a second "Bodyguard" movie. "I told her I would take of her just the same way that I took care of Whitney."

While it may sound like a pipe dream -- the famous former royal in a Hollywood film -- Costner told Cooper the princess was serious about it. ""She wanted me to write it for her," he said. "I said 'I'll tailor it for you if you're interested.' She goes, 'I am interested.'"

Like the first film, Costner would play a bodyguard who protects a famous woman from paparazzi and stalkers and then becomes romantically involved with her. He told Cooper he received a draft of the script for the proposed sequel on Aug. 31, 1997, the day before Diana's fatal Paris car crash.

Related content:

• Houston death investigation closed
• Houston 911 call: 'Irate' woman kept hanging up
• Dr. Drew still thinks foul play could be involved
• Silverstone defends pre-chewed food video
• $23K per month not enough for Etheridge ex
• Thomas Kinkade's cause of death may be unknown for months