When Leonard Nimoy, who played Spock in the extremely popular "Star Trek" franchise, was photographed in a wheelchair last month, fans immediately became worried about the 82-year-old's health.

The actor revealed last week that he has been diagnosed with COPD (Chronic Obstructive Pulmonary Disease), a severe lung condition that is often linked to smoking.

Nimoy wrote that although he quit smoking 30 years ago, it was "not soon enough."

The popular actor signs all of his tweets LLAP, an abbreviation of his character's trademark phrase "live long and prosper."

A week after he shared his diagnosis, Nimoy writes he is "doing OK. Just can't walk distances."

According to the National Institutes of Health, the ailment is the third leading cause of death in the U.S. and causes coughing, wheezing, shortness of breath and chest tightness.

Though there is no cure for COPD, there are medications that can help relieve symptoms and keep the condition from worsening.

Nimoy rose to fame in the '70s while playing Spock, the half-human, half-Vulcan commander of the starship Enterprise in the "Star Trek" series.

leonard nimoy

Nimoy as Spock in the "Star Trek" series

He most recently appeared in J.J. Abrams' "Star Trek Into Darkness" last year.