The former Boston College baseball star was diagnosed with amyotrophic lateral sclerosis on March 13, 2012 -- and was told at the time he had five years to live. Frates has since dedicated himself to raising money and awareness about ALS.
The "Team FrateTrain" Facebook page showed a post from Sunday saying Frates was back at Massachusetts General Hospital fighting the disease.
RELATED: Pete Frates through the years
Pete Frates through the years
Pete Frates through the years
BOSTON - APRIL 25: Boston College's Pete Frates holds up his glove after making a diving catch robbing Harvard's Chris Mackey of a base hit during fourth inning action at Fenway Park on Tuesday, April 25, 2006. (Photo by Matthew J. Lee/The Boston Globe via Getty Images)
BOSTON - JUNE 10: Boston Red Sox player Brock Holt, far right, talks with members of the media about Pete Frates, who sits with his family at left, during a ceremony at Fenway Park in Boston on Jun. 10, 2017. Frates is the inspiration for the Ice Bucket Challenge to raise money for amyotrophic lateral sclerosis research, and is donating a cap and glove from his playing days at Boston College, and the bucket and sunglasses from his 2014 Ice Bucket Challenge, to the National Baseball Hall of Fame in Cooperstown, NY. (Photo by Matthew J. Lee/The Boston Globe via Getty Images)
BOSTON - AUGUST 29: Julie Frates holds her husband Pete Frates at a fund raiser celebrating ALS Awareness Month in Boston on Aug. 29, 2016. Pete Frates is credited with creating the ice bucket challenge to raise money for ALS research. (Photo by Keith Bedford/The Boston Globe via Getty Images)
BOSTON, MA - OCTOBER 1: Former Boston College Eagles baseball player and creator of the Ice Bucket Challenge Pete Frates takes part in pregame ceremonies honoring David Ortiz #34 of the Boston Red Sox at Fenway Park on October 1, 2016 in Boston, Massachusetts. The Blue Jays won 4-3. (Photo by Rich Gagnon/Getty Images)
BOSTON, MA - OCTOBER 1: David Ortiz #34 of the Boston Red Sox is reacts with ALS survivor Pete Frates during a retirement tribute ceremony before a game against the Toronto Blue Jays on October 1, 2016 at Fenway Park in Boston, Massachusetts. (Photo by Billie Weiss/Boston Red Sox/Getty Images)
BEVERLY, MA - DECEMBER 13: Pete Frates, center, is surrounded by Boston College baseball players and his brother Andrew Frates, right, after receiving an award from the NCAA at his home in Beverly, Mass., on Dec. 13 2016. Frates is a former BC baseball player and the face of the Ice Bucket Challenge for ALS. (Photo by John Blanding/The Boston Globe via Getty Images)
BOSTON - AUGUST 14: Red Sox manager John Farrell gets together on the field with Pete Frates, former Boston College baseball captain who has ALS and is behind the ice bucket challenge that has gone viral. Farrell and third baseman Will Middlebrooks, not pictured, also took the ice bucket challenge. (Photo by Barry Chin/The Boston Globe via Getty Images)
BEVERLY, MA - SEPTEMBER 13: Pete Frates after an effort to break the world record for number participants in an Ice Bucket Challenge during events celebrating the dedication of Peter Frates Hall at Endicott College in Beverly, Mass., Sept. 13, 2016. (Photo by John Blanding/The Boston Globe via Getty Images)
BOSTON, MA - OCTOBER 1: ALS survivor Pete Frates is introduced before a retirement tribute ceremony for David Ortiz of the Boston Red Sox before a game against the Toronto Blue Jays on October 1, 2016 at Fenway Park in Boston, Massachusetts. (Photo by Billie Weiss/Boston Red Sox/Getty Images)
BEVERLY, MA - SEPTEMBER 13: Pete Frates; Julie Fates, his wife; and their daughter Lucy, wait for students and others at Endicott College attempt to break the world record for participants in the Ice Bucket Challenge at the college in Beverly, Mass., on Sept. 13, 2016. The school also dedicated a building as Pete Frates Hall. (Photo by John Blanding/The Boston Globe via Getty Images)
BOSTON, MA - AUGUST 10: Governor Charlie Baker chats with Pete Frates after he and various Boston political members participated in the ALS ice bucket challenge on the steps of the state house on Aug. 10, 2015. (Harrison Hill for The Boston Globe via Getty Images)
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In 2014, Frates wrote of his commitment to raising awareness -- which included creating the world-famous Ice Bucket Challenge -- saying his "calling" was to "raise ALS awareness and to fight for a brighter future for all those affected today and those yet to come."
"My dream is for this article to be found by someone in a Google search one day—much like the one that linked my symptoms to ALS," Frates wrote, "And for he or she to wonder how anyone ever could have died from something treated so easily."