Mel Gibson could not attend Whitney Houston's funeral.

Mel Gibson is one of the celebrities who was invited to Whitney Houston's funeral on Saturday, February 18, OnTheRedCarpet.com has learned.
However, the 56-year-old actor is unable to make it due to "family plans," TMZ reported.

"He was invited but any comment beyond that is speculation as to reasoning," Houston's spokesperson told OnTheRedCarpet.com on Friday.

Gibson's rep declined to comment, saying details about the funeral would have to be given by the singer's family. TMZ said the actor had in the past tried to help Houston combat her substance abuse.

Houston died at age 48 in a room at the Beverly Hilton hotel in Beverly Hills, California on February 11. Prescription drugs were found on the scene. The cause of Houston's death has not yet been revealed.

Her funeral will be private and a select number of celebrities have been invited to attend. The confirmed guest list includes Kevin Costner, who played Houston's love interest in the 1992 movie "The Bodyguard," the singer's godmother Aretha Franklin and her mentor, music producer Clive Davis (see who else is set to attend Whitney Houston's funeral).

Houston and Gibson have not starred together in an on-screen project. They have, however, dealt with similar personal issues. Both have battled substance abuse and marital problems.

Houston's relationship with ex-husband Bobby Brown, father of their daughter Kristina Bobbi, was turbulent and she even filed a charge of domestic abuse against him in 1992. They divorced in 2006 and underwent a custody battle over their daughter, who is now 18.

Last year, Gibson dealt with a custody battle and domestic violence case involving his ex-girlfriend and mother of his eighth child. In 2010, recordings of a phone conversation between the two were posted on RadarOnline and a man that sounds like him was heard making threats against her and hurling racial slurs against black and Hispanic people. Gibson later said the tape was edited, a claim his ex denied.

In December, he finalized what appeared to be an expensive divorce settlement with long-estranged wife Robin, the mother of his other seven kids.

Gibson became a tabloid favorite after reportedly unleashing a tirade of anti-Semitic comments during a 2006 drunk driving arrest. He later went through rehab to combat an alcohol addiction.

Investigators have not revealed what killed Houston, who was found unconscious and underwater in a bathtub by a member of her staff. Her autopsy has been completed but the results will not be released until a toxicology report is produced, which could take up to eight weeks.

The Los Angeles County Coroner's Office recently issued subpoenas for Houston's medical and pharmacy records in a routine move that could speed up its investigation. Assistant Chief Coroner Ed Winter said "a number of doctors" were contacted.

He had previously confirmed that bottles of prescription drugs were found near Houston's body on the day she died. A source close to the matter told OnTheRedCarpet.com that one of them was the antibiotic amoxicillin.

Mixed with alcohol, some medications can cause death. It is unclear what substances Houston ingested on the night she died. The singer, who underwent a rehab stint in May 2011, was spotting drinking champagne the night before her death, according to witnesses.

Two days before she died, she celebrated and performed at a Los Angeles nightclub in what marked her final performance, although it is unclear whether she consumed alcohol.