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The long-serving soap actress, who has played practice manager Julia Parsons for almost a decade, will bow out of the programme next month.
Keen told What's on TV: "It's been a heck of a ride and a huge learning curve. There are so many people I'm going to miss. But we will always keep in touch.
"Julia has had a tough time over the years, but she has always come through with grace and humour. While she doesn't suffer fools, she does have a heart of gold and a great sense of humour. So whatever happens, here's to Julia's future happiness!"
Julia has recently embarked on a romance with garage owner Martin Millar, but will reportedly be offered a new job away from Letherbridge.
It is currently unclear whether she will depart with Martin or leave with a broken heart.
Keen, who joined Doctors in 2003, will leave the show on May 18.
> Doctors star Diane Keen speaks to Digital Spy
> More Doctors news and spoilers
