Meredith Grey's love affair with Dr. McDreamy is back on... George O'Malley starts his internship — again... and an injured deer gets treated in the ER!

Welcome to Season 4 of ABC's smash hit Grey's Anatomy. The ENQUIRER has an exclusive sneak peek at the upcoming plot twists on TV's top-rated hospital drama.

One big surprise unfolded off-camera when a skunk wandered onto the set while Dr. McDreamy was popping the question to Meredith Grey — played by Patrick Dempsey and Ellen Pompeo, according to an ABC insider.

"Derek Shepherd was telling Meredith: 'I want to grow old with you...I want to spend the next 108 winters with you,' when a production assistant noticed the skunk," the source said.

"The timing was hysterical. Patrick was right in the middle of this big emotional scene, but everyone's eyes were focused on the skunk!"

After a few minutes, crew members chased the skunk off the lot "without triggering a major stink," the source cracked.

The new season finds a humbled Dr. George O'Malley (T.R. Knight), who failed his exam during last season's finale, now repeating his internship under Meredith's supervision.

New regulars on the show include Richard Keith as Mitch Greenberg, who interns under the supervision of Katherine Heigl's character, Dr. Isobel "Izzie" Stevens.

Another new intern — Meredith's TV half sister Lexie Grey — will be played by actress Chyler Leigh.

"Fans will remember Lexie as the girl who unknowingly flirted with Dr. McDreamy — and sparked his interest," said the source.

Tymberlee Chanel and Gloria Garayua also join the cast as new interns — and get a quick dose of reality.

"Shortly after their arrival, a three-car accident sends multiple casualties into Seattle Grace," the insider continued.

"And on the very first day on the job, one intern helps deliver a baby."

But the winner of the "Strangest-Patient-Ever-Admitted-To-Seattle-Grace" award goes to a bleeding deer hit by a car and handed over to the ER docs for treatment, said the source.