Dame Barbara Windsor, 81, joined her husband Scott Mitchell, 55, and Adam Woodyatt, who plays Ian Beale, 50, in the royal box at the show to watch EastEnders star Bonnie Langford perform.
The actress’ rare outing comes after her spouse, who has been married to her for 18 years, revealed she had been diagnosed with Alzheimer’s disease four years ago.
Refusing to the let the condition take over, she was seen smiling for pictures alongside her group and even had a go at tap dancing alongside Bonnie.
Adam, who was also joined by his wife Beverley, filmed the actress receiving a standing ovation from the crowd as she waved to fans.
Taking to his Instagram page with 11,000 followers, he uploaded the clip with the caption: “Incredible day out with @beverleywoodyatt Scott and the legend that is Dame Barbara at #42ndstreet.
“During interval we sneaked her into Royal Box and the response from the auditorium was so moving.
“After the show, she was even tap dancing on the stage. A day I will always remember.”
Scott also said he enjoyed seeing the “old Bab emerge for a while” during their evening out.
He told The Mirror: “It gives her such pleasure chatting to everyone and seeing them all and she never expects that reaction.
“Then she did an impromptu dance routine on the stage after the show.
“It’s like two different people once she enters a theatre. The old Babs emerges for a while. It’s wonderful to see those moments.”
Back in May, Scott spoke openly about Dame Barbara’s Alzheimer’s for the first time, four years after her diagnosis.
Speaking to The Sun, he revealed she is taking medication for the degenerative brain disease.
Recalling the moment Dame Barbara was first diagnosed, he revealed the Carry On star broke down in tears.
He said: “When the doctor told us, she began crying then held it back, stretched her hand out to me and mouthed, ‘I’m so sorry.’
“I squeezed her hand back and said, ‘Don’t worry, we’ll be OK’.”
Scott also explained his reasons for speaking out, adding: “I hope speaking out will help other families dealing with loved ones who have this cruel disease.
“Secondly, I want the public to know because they are naturally very drawn to Barb ara and she loves talking to them.
“So rather than me living in fear she might get confused or upset, they’ll know that if her behaviour seems strange, it’s due to Alzhei mer’s and accept it for what it is.”
He added Barbara’s conditions had become “a lot more difficult for us to hide”.