In sneak peek pictures, Lacey and Gillian can be seen sharing a giggle in between filming scenes for the BBC One soap.
The pair filmed their first scenes together this week. Gillian's reappearance ties in with Lacey's permanent return to EastEnders as Stacey Branning later this year.
Gillian, who plays Stacey's mum Jean Slater, last appeared on the show in September 2013 when she left Walford to start a new life with her boyfriend Ollie. Jean's last scene with Stacey was on Christmas Day in 2010.
Although Jean's return to Albert Square is being kept under wraps, the teaser pictures show Stacey - who is accompanied by a prison guard - visiting bipolar sufferer Jean in hospital.
Viewers will remember that following Stacey's initial return to EastEnders in February this year, she confessed to the murder of Archie Mitchell, and is currently awaiting trial.
Actress Gillian announced her return to the soap last month. Although it will only be for a short stint, it was welcome news for fans of the soap who miss watching Jean and Stacey's mother and daughter relationship on screen.
Gillian said at the time: "The storyline promises to be challenging and exciting! I look forward to playing again with old friends and new and to pick up the special relationship between Stacey and Jean."
Executive producer Dominic Treadwell-Collins also said: "We are so pleased to have Gillian back with us to reprise her role as Jean Slater, albeit briefly. Stacey and Jean have such a rich, loving but difficult history.
"There is still so much to plumb between them as we delve deeper into what it means to have bipolar disorder as a mother but also as a daughter. There are some truly heartbreaking scenes ahead for our audience."
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