Nancy McKeonis reeling after the death of her beloved brother, fellow child starPhilip McKeon.

Philip, 55, died Tuesday morning after a battle with a long illness. A source tells PEOPLE that theFacts of Lifeactress 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 tributeto Philip, thanking him for his support during the “tough time.”

Ron Galella Collection via Getty

Nancy McKeon and Philip McKeon

“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

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

Philip is best known for his role as Tommy Hyatt onAlice, in which he starred opposite Linda Lavin from 1976-1985. The CBS sitcom was based on Martin Scorsese’s 1974 rom-comAlice 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.

source: people.com