Gray, who played Sue Ellen Ewing, the wife of Hagman's backstabbing oil magnate J.R. Ewing in the legendary TV drama, was with her friend and co-star when he died in a Texas hospital.
She released a statement late on Friday, in which she called the star "my best friend for 35 years," adding, "He was the Pied Piper of life and brought joy to everyone he knew. He was creative, funny, loving and talented, and I will miss him enormously."
Gray helped Hagman battle throat cancer last year (11), suggesting he give up eating meat.
Duffy, who played Hagman's onscreen brother Bobby Ewing, took to Twitter.com to post a photograph of the two actors sharing a smile, alongside the poignant message, "My friend is taking a break. Pardon my silence. Love Patrick."
Principal, who starred as Duffy's wife Pamela Barnes Ewing in the show, tells UltimateDallas.com, "Larry was bigger than life... on screen and off. He is unforgettable, and irreplaceable, to millions of fans around the world, and in the hearts of each of us, who was lucky enough to know and love him. Look out God... Larry's leading the parade."
Kercheval, J.R. Ewing's arch nemesis Cliff Barnes in the show, writes on Twitter, "A friend and long time partner... the other half... RIP Larry Hagman... your spirit will live long."
Hagman's other onscreen wife Barbara Eden, who starred with him in sitcom I Dream Of Jeannie, has also paid tribute to the actor, revealing they recently reconnected and she feels grateful to have been able to spend that time with him.
In a post on her Facebook.com page, she writes, "I still cannot completely express the shock and impact from the news that Larry Hagman has passed... I am so thankful that this past year I was able to spend time with him and experience yet again 'Larry' in all his Big Texas bravado... I, like many others believed he had beat Cancer and yet we are reminded that life is never guaranteed. My deepest condolences go out to his (family)... I can honestly say that we've lost not just a great actor, not just a television icon, but an element of pure Americana. Goodbye Larry, there was no one like you before and there will never be anyone like you again."
Hagman recently told the Los Angeles Times of his final wishes, revealing he wanted his remains to be scattered over a field and "have marijuana and wheat planted and harvest it in a couple of years and then have a big marijuana cake, enough for 200 to 300 people. People would eat a little of Larry."