There’s no dodging the issue — all of the Glee characters who were juniors this past season will graduate from McKinley High in May 2012, with their portrayers (presumably) leaving the show.

Speaking on Ryan Seacrest’s radio show Friday morning, Glee creator Ryan Murphy held firm to his previously revealed transition plan, saying that for original characters such as Rachel, Finn, Quinn and Puck, “This next [season] will be their senior year, and then that [they] will graduate.”

“We didn’t want to have a show where they were in high school for eight years,” he explained. “We really wanted to be true to that experience.”

To proactively fill the void (Murphy said he’s loath to use the words “eliminating or replacing”), brand-new, younger characters will be woven into McKinley’s ranks over the coming season — a few in the fall, and a couple more at midseason. Only one of the newbies, however, will be the product of the Glee Project reality show now airing on Oxygen.

Glee Recruits Buffy Vet Marti Noxon Plus Five New Writers

“There’s a couple rumors floating around, that half the cast is go to be replaced by the winner of The Glee Project, which is not true,” Murphy told Seacrest. Rather, only the singular winner of that reality competition will join Glee, for at least seven episodes.

Eye On Emmy: Glee Star Chris Colfer’s Comedy Kudos Quandary, ‘I Cry In Every Episode!’

Murphy notes that while his original young cast will leave “sort of an indelible mark,” he is looking forward to the challenge of introducing America to a new wave of relatively unknown talents poised to generate fresh buzz (and, who knows, maybe land in a controversial Rolling Stone layout). Besides, not everyone is leaving; Murphy envisions Matthew Morrison and Jane Lynch as “the male and female lynchpins of the series” even as young’uns come and go.

But, he says, Glee “is a celebration of youth and talent and … finding those young unknown people and giving them an opportunity to break into the business and become stars is a really fun and exciting thing, and is the spirit of the series.”