Mormon President Thomas S. Monson, 90, won't attend this weekend's church conference because of deteriorating health — marking the first time in more than a half century that the longtime church leader won't deliver spiritual guidance at the important twice-yearly event.

Monson's absence was confirmed Thursday by church spokesman Eric Hawkins, who referred to a previous statement in May that revealed Monson was no longer going regularly to meetings at church offices because of limitations related to his age.

Monson, who in 2008 became the 16th president of The Church of Jesus Christ of Latter-day Saints, is considered a prophet, seer and revelator. He oversees the religion's church and business operations with help from two top counselors and members of the Quorum of the Twelve Apostles.

He has delivered speeches at every one of the twice-yearly conferences since 1963, when he became the youngest member ever of the Quorum of the Twelve Apostles, Hawkins said.

Mormon presidents serve until they die.

Monson has scaled back conference participation recently and gave just two short speeches at April's conference. He was hospitalized afterward when he reported "not feeling well."

The religion also announced Thursday that Robert D. Hales, 85, a member of the Quorum of the Twelve Apostles, won't be at the conference either due to ailing health. Hales was taken to hospital several days ago for treatment of pulmonary and other conditions, Hawkins said.

A native of New York City, Hales was a fighter pilot in the Air Force and business executive before being named to the Quorum of the Twelve Apostles in 1994.

Monson will be the first church president since 1994 not to attend and make at least one speech, according to the church-owned Deseret News.

But prior to that, it was fairly common for church presidents to miss conference toward the end of their lives.

President Ezra Taft Benson didn't attend or wasn't able to speak at conferences for several years before his death in 1994. President Spencer W. Kimball wasn't able to speak at his final conference in October 1985 before his death the next month.

The conference brings 100,000 people to Salt Lake City on Saturday and Sunday for five sessions where top church leaders give spiritual guidance and deliver church news. Millions more watch live broadcasts from their homes.

Monson and Hales are among six of the religion's top 15 leaders who are 84-years-old or older.

The man next in line to become president, Russell M. Nelson, is 93.

Following a church succession plan that was established in 1889, Nelson would take over as the longest-tenured member of the Quorum. Nelson, a former surgeon who joined the Quorum in 1984, is expected to attend and speak at the conference.

Church officials say the orderly process prevents any lobbying internally or publicly and reflects the religion's culture that frowns on personal aspiration for leadership.