Sad news for fans of Matt Smith - he's leaving Doctor Who at the end of the year, it's been announced by the BBC.
Matt said in a statement: "Doctor Who has been the most brilliant experience for me as an actor and a bloke."
He'll feature in November's 50th anniversary special episode before making his final appearance in the Christmas special, when we'll see the Doctor regenerate.
The BBC promises a "spectacular exit" for Matt - but it's being kept tightly under wraps!
What's your favourite Matt Smith moment?
Matt Smith has been on our screens as the Time Lord since 2010.
In that time, he's fought baddies such as Daleks, Cybermen, Weeping Angels and the Silence.
He's also shared his adventures with Amy Pond (Karen Gillan), Rory Williams (Arthur Darvill) and, most recently, Clara Oswald (Jenna-Louise Coleman).
But what's YOUR favourite Matt Smith moment from the show?
And who do you reckon should take over the role?
This chat page is now closed but you can read some of the comments that were sent in below.
"In The Beast Below I love it when Matt Smith says, 'If this is just the mouth I'd love to see the stomach. Though not right now.'"
Andalucia, Cockermouth, England
"I am truly devastated about Matt leaving. Since that day David regenerated into Matt I fell in love with the show, and it has been a big part of my life ever since!"
Fern, Barry, Wales
"I hope the new Doctor will be Colin Morgan from Merlin."
Ryan, Gateshead, England
"He has been an amazing Time Lord. I can't get enough of his bow tie and odd dress sense."
Nadine, Littlehampton, England
"I think Steven Gerrard should be the next Doctor, like a footballing Time Lord."
Kian, Llangefni, Wales
"I think Matt was a good Doctor but no one can beat David Tennant."
Callum, Cumbria, England
"It's really sad to see Matt Smith go but I think Benedict Cumberbatch from Star Trek and Sherlock should play the 12th Doctor, as he did a very good job in his other roles."
Maryam, Leicestershire, England
"My favourite moment is when he handed a key to the Tardis to Clara in the Christmas special. But then Clara got snatched by the ice women."
Kay, Birmingham, England
"I think Dani Harmer should be the new Doctor because she is a very good actress."
Vic, London, England
"Matt Smith has played an amazing role as the Doctor. My favourite moment was when he said I need a cup of coffee, 12 Jammie Dodgers and a fez. Bow ties are cool."
Tom, Oldham, England
"I like it when he always says 'Run'!"
Lulu, Bristol, England
"My favourite moment was when Matt Smith first appeared in The End of Time Part Two, when he regenerated from David Tennant to himself and talked to himself about not being ginger or having girls' hair, and having fingers and feet."
Byron, Sudbury, England
"My favourite bit was when the Doctor said, 'I'm armed... with a screwdriver'."
Samuel, Deddington, England
"My favourite bit was when he just met Amy. It was funny and weird at the same time. When David Tennant left I cried but I'm going to cry more for Matt Smith. I will miss you Matt Smith."
Ellie, Huddersfield, England
"When he was half Cyberman in the latest Cyberman episode, and he kept changing between the Cyber Doctor and the real Doctor!!"
Ellen, Bristol, England
"Fish fingers and custard!"
Jo, Chepstow, Wales
"I think Olly Murs should be the Doctor, but a singing one."
Isaac, Haverfordwest, Wales
"I think Jim Carrey should replace Matt Smith as he is quite bonkers and would suit an alien character."
Ben, Torquay, England
"I love listening to Doctor Who, sad to hear him leave. But luckily as I'm blind I still have the audio books to listen to. Thank you Matt for making television so magical."
Louis, Bradford, England
"I think Tommy Knight from The Sarah Jane Adventures and Waterloo Road should be the next Doctor because he already knows a lot of the monsters."
Chloe, Grimsby, England
"My favourite moment was The Name of the Doctor which I really enjoyed."
Bradley, London, England
"I think the best Matt Smith moment is just after he's regenerated and he's checking whether he's got arms and legs. I think there should be a degeneration back to David Tennant."
Tomos, Ruthin, Wales
"When David Tennant changed into Matt Smith and when he appeared in The Sarah Jane Adventures."
Lucas, Hereford, England