BBC One soap EastEnders has suffered its lowest ever audience, averaging just 3.9 million viewers up against an hour-long special of ITV1's Emmerdale.
Richard has played Pauline Fowler since the show's 1985 launch
Emmerdale averaged 6.7 million during EastEnders, and 6.6m overall, according to unofficial overnight figures.
An EastEnders spokeswoman said the figures were "entirely untypical" and its average audience was 10 million.
ITV1 reality show Love Island drew two million from 2200 BST, while Channel 4's Big Brother attracted five million.
The figures for Thursday's episode of EastEnders were down from 5.2 million on Tuesday, which had been a record low.
"EastEnders is a show in good health which has had a strong year both critically and with audiences," the spokeswoman said.
"EastEnders reaches over 19 million people each week, and the average audience per episode is 10 million. Last night's figures were entirely untypical."
Original cast member Wendy Richard, who plays Pauline Fowler, announced this week she was leaving the show after 21 years.