'Facts of Life' Star Nancy McKeon Is 'Devastated' over Brother Philip McKeon's Death: Source

Philip McKeon died Tuesday morning after battling a longtime illness

Nancy McKeon is reeling after the death of her beloved brother, fellow child star Philip McKeon.

Philip, 55, died Tuesday morning after a battle with a long illness. A source tells PEOPLE that the Facts of Life actress is struggling to come to terms with the unimaginable loss.

"She's devastated. She and Philip were very, very close," the source says. "The whole family is going to cling together and find comfort in each other during this time. My heart goes out to them."

Philip's death comes less than two months after their father, Donald McKeon, died in October.

Just weeks before Philip's death, Nancy, 53, dedicated a heartfelt birthday tribute to Philip, thanking him for his support during the "tough time."

Nancy McKeon and Philip McKeon
Ron Galella Collection via Getty

"A huge happy birthday to my big brother!!" she wrote on Nov. 11. "It's been a tough time lately… but as we've always said…we'll get through it together…love you Dude….and as always… our humble thanks to all our veterans."

Philip McKeon
Bobby Bank/Getty

McKeon spokesman Jeff Ballard confirmed Philip's death to PEOPLE in a statement Tuesday.

"We are all beyond heartbroken and devastated over Phil's passing," Ballard said. "His wonderful sense of humor, kindness and loyalty will be remembered by all who crossed his path in life."

Philip is best known for his role as Tommy Hyatt on Alice, in which he starred opposite Linda Lavin from 1976-1985. The CBS sitcom was based on Martin Scorsese's 1974 rom-com Alice Doesn't Live Here Anymore, in which Alfred Lutter played the titular character Alice Hyatt's son Tommy. However, Philip replaced Lutter after the pilot.

Following his role on the sitcom, he worked at Los Angeles station KFWB News 98 in its news department for 10 years before later moving to Wimberly, Texas, where he hosted his own radio show and relocated to be closer to family. Charlie Sheen honored Philip, his costar in an episode of the 1980s NBC anthology series Amazing Stories, on Twitter. "Shared some wonderful moments in the 'trenches' with Phil McKeon many moons ago," wrote Sheen, 54. "Over the past few decades, he was always a perfect gentleman and an ebullient spirit."