(CNN) -- Sean Sasser, whose relationship with the late Pedro Zamora on MTV's "The Real World: San Francisco" broke cultural barriers on U.S. television, has died, his longtime partner told CNN on Thursday. Sasser was 44.
Sasser, who had been HIV positive for 25 years, died Wednesday from mesothelioma, a rare form of lung cancer that was diagnosed just last month, Michael Kaplan said. He died in the Washington home he shared with Kaplan.
Sasser was not one of the original cast members but became a household name as his relationship with Zamora was explored during the show's third season in 1994. The couple's exchange of vows during a commitment ceremony, the first ever broadcast on U.S. television, became a landmark moment in TV history.
The couple began dating during the taping of the series. Their relationship and Zamora's battle with AIDS while living in "The Real World" house with seven strangers became must-see-TV for teens and young adults, many of whom had never been exposed to a gay couple, much less someone living with HIV.
Zamora, who had been diagnosed with AIDS at age 17, was a well-known AIDS activist at the time he was cast on the show at age 21. Sasser, who was also working as an activist and educator, also revealed on the show that he was HIV positive.
During the taping of the series, Zamora's health took a turn.
"This wasn't a romantic death. It wasn't a heroic death. It was horrible, and Sean couldn't do anything except watch it happen," fellow co-star Judd Winick told the online magazine POZ in 1997. Winick chronicled his friendship with Zamora and Sasser in the graphic novel "Pedro and Me: Friendship, Loss and What I Learned."
Zamora died on Nov. 11, 1994, with Sasser at his side just hours after the airing of the final episode of the season, which featured the two men exchanging their vows, according to MTV.
Sasser continued his work as an AIDS activist and educator.
Sasser recently moved from Portland, Oregon, to Washington when Kaplan took a job with AIDS United, a non-profit group. The couple had dated off and on for years since the 1990s, but moved in together about six years ago, Kaplan said.
Sasser was a pastry chef at RIS, a Washington restaurant, but he was unable to work for the last five weeks, Kaplan said. His last week was spent in bed at home, his partner said.
His illness evolved quickly, with the July diagnosis of stage 4 mesothelioma following a June blood test showing an abnormality, Kaplan said.
News of Sasser's death spread quickly across social media, with Winick posting a series of photos of Sasser and Zamora via Twitter.
Actor and gay rights activist Wilson Cruz wrote on Twitter: "My heart breaks. Another beacon of light in our community is darkened tonight with the passing of Sean Sasser."
"It is because of Pedro and Sean that I made safe decisions about protection and partners in 1993 at just 15. Thanks," Yasemin Abdulraouf wrote in a post on Twitter.
Another person, identified by the Twitter handle Hollis, wrote: "U & Pedro showed true grace & dignity in the face of adversity. Hope u have found peace."
MTV wrote, simply: "RIP to a member of the MTV family, groundbreaking Real World star + AIDS activist."
CNN's Rachel Wells contributed to this report.