No one associated with One Tree Hill is happy about the departure of stars Chad Michael Murray and Hilarie Burton.

But CW entertainment president Dawn Ostroff is attempting to spin it as well as possible.

"A show going into its seventh year is very open to reinventing itself," Ostroff told reporters at The CW's upfront presentation. "And one thing I have to give [series creator] Mark Schwahn a lot of credit for is that he has kept the show so fresh all these years."

As previously reported, One Tree Hill hopes to "replace" Lucas and Peyton by adding a trio new characters, including Haley's older sister, Quinn.

"We look at shows like ER, shows that go on for many, many years, and a lot of those casts go through different people," said Ostroff. "So we are sad to see [Chad and Hilarie] go — and grateful for everything they did for the show — but excited about seeing who else is going to join the cast."

Matt Richenthal is the Editor in Chief of TV Fanatic. Follow him on Twitter and on Google+.