Logan Stevenson, 2, died Monday night at home in his mother's arms. His mother, Christine Swidorsky Stevenson, made the announcement on Facebook.
"He is with angels and he's in no more pain," she said on the social networking site. Logan had leukemia and other complications.
Swidorsky shares the home in Jeannette, about 25 miles east of Pittsburgh, with her new husband, Sean Stevenson, where they were wed on Saturday. The child donned a tan pinstriped suit and was carried into the ceremony by his mother.
According to the Facebook post, the boy's breathing became labored before his mother called a hospice worker, who informed the couple that Logan was dying.
"Sean and I held him all day he was comfortable with his medication then at 8:18 my son took his last breath in my arms," his mother wrote.
She also thanked those who supported the couple during the boy's illness and wedding plans.
"We love all of u for all your prayers thank u all for caring god bless u all!" she wrote. "And most of all god bless Logan I'll c u in my dreams my son."
The couple initially planned to be married next July, but moved up their wedding date when they learned late last month that Logan only had a few weeks left to live. They wanted Logan to see them get married and to be part of family photos.
Logan was born Oct. 22, 2010. Shortly after his first birthday, he was diagnosed with acute myeloid leukemia. He had Fanconi anemia, a rare disease that often leads to cancer.
He underwent a stem cell transplant in July 2012, and had a kidney removed last March that was ravaged by a tumor.
During a trip to Disney World in June, the boy fell ill. He was hospitalized in Florida before he was flown back to Pittsburgh.
During a trip to the emergency room last month, a test revealed a mass in his remaining kidney, which led to his terminal prognosis.
The boy's parents kept Logan at home in his final days, after doctors told them he'd likely be more comfortable there, provided he was properly medicated.
The Associated Press contributed to this report.