However, it was also announced that Molly will not be reprising her role and Milly Zero will be taking over.
Molly, who played Dotty from 2008 until 2010 revealed that she was approached by soap bosses over the return, but only to explain why she wasn't being brought back.
The 18-year-old told The Sun Online: "They did approach me, unfortunately they wanted the new Dotty to go back and appear a lot older and be played by someone in their 20s.
"Of course I would have loved to have returned to EastEnders, but I believe everything happens for a reason."
Of course I would have loved to have returned to EastEnders, but I believe everything happens for a reason.
Following the recast news, actress Milly said: "I am honestly so excited to be playing Dotty Cotton and joining the E20 family.
"Especially playing alongside June Brown, who I have been watching on my telly since I was a young girl.
"Her and Dotty have such an interesting relationship to explore with a complicated history, so I can't wait to see what the future holds for them.
"It feels very surreal and I am buzzing already!"
Executive Producer Jon Sen added: "We're all super-excited to welcome Dotty back to the Square - sharp-witted and with an eye for human weakness, she's not afraid to say what she thinks.
"We are also thrilled that Milly will be taking on the role - her versatility as an actress and ability to capture Dotty's blend of sass, intelligence and vulnerability ensure that Dotty will return with a bang this autumn."
The return of Dotty means legend June Brown - aka Dot Branning - will also be back, after an absence of some months.
Dotty is coming back to attend university and quickly makes an impression on other Square residents.
Dotty originally arrived with her troublesome father Nick on Boxing Day 2008.
Dot soon realised her son didn't have a job and he and Dotty were living rough.
Nick said he would either put Dotty into care or sell her to Dot and after serious consideration Dot bought her granddaughter to get her away from her father.
During her time on Albert Square, Dotty proved to be trouble, throwing Tiffany Butcher's bridesmaid dress and MP3 player in the bin, telling her father about Dot's will and teaming up with him to plot Dot's murder.
In 2010, Dotty's mother Sandy showed up and at first Dot assumed she was from Social Services.
She revealed she was looking for her daughter Kirsty and as soon as Dot saw the photo, she realised Kirsty was Dotty.
Dotty admitted she missed her mother and Dot revealed to her that her mum was alive and Nick had lied to her.
When Dot called Sandy and she turned up, Dot told her granddaughter she should go with her mother and they said an emotional goodbye.
EastEnders is on Mondays and Fridays at 8pm and Tuesdays and Thursdays at 7.30pm.
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