Pat's reappearance is part of an ongoing dementia storyline centred on Nigel Bates, with scenes transporting him back to the 1990s as his memory fades.
The character, who died of cancer in 2012, will offer support to Nigel at The Queen Vic as his dementia symptoms escalate.
Clement, 83, expressed her surprise and excitement at being asked back, describing it as “just like coming home”.
EastEnders has collaborated with Dementia UK for this storyline, which features Nigel's diagnosis with young onset dementia.