The phrase "a longtime collaborator of" is a correct and usable phrase in written English.
You can use it when referring to someone who has been working with another person on the same project for a significant period of time. For example, "Karen has worked alongside Bob as a longtime collaborator of his for the past five years."
Gurf Morlix, a longtime collaborator of Ms. Williams's, produced Ms. Gauthier's latest album, "Filth & Fire".
(Mr. Rudd, a longtime collaborator of Mr. Wain's, also helped write the script).
Ian Rickson, a longtime collaborator of Mr Butterworth's, directs.Seven years ago Mr Butterworth quit London for the country.
(The excellent director of photography is Yorick Le Saux, a longtime collaborator of the French filmmaker Olivier Assayas).
She marries this man, a longtime collaborator of her grandmother who is nearly 30 years her senior.
Ms. Robinson, a longtime collaborator of Mr. Cohen's, also sang a solo feature, "Boogie Street," with authority.
Brenda Bufalino, a longtime collaborator and student of Coles's, gave a few snippets of her delicate and silky style, and Hank Smith was his usual understated self in a riff off Charles (Cookie) Cook's choreography.
"He's about as much an outdoorsman as Woody Allen," said a longtime collaborator, Dr. O. H. Frazier of the Texas Heart Institute.
Jaeger-LeCoultre outsourced the ambitious project to Jérôme Boutteçon, a longtime collaborator and master of marquetry, which uses inlaid materials to create an image.
With Dr. Marguerite Vogt, who became a longtime collaborator, he developed a method of determining the amount of polio virus present in cell culture, a step that was essential to development of the Sabin polio vaccine.
Reassuringly, those costumes and the sculptural set are the work of Barbara Kilpatrick, a longtime collaborator whose delicately powerful designs create the perfect worlds for Ms. Shick's intimate, poetic distillations of time and place.
