Dyer's character Mick Carter is believed to have drowned during the Christmas Day special while Brooks' Janine Butcher was arrested the following day.
Now Cassidy, who plays long-serving character Sonia Fowler, has the sung the praises of her two former co-stars.
Posting a picture of the three of them, Cassidy wrote: "@officialdannydyer @charlie_brooks_xx the love I have for these two. Smashed it."
She added: "I shall miss you but know we will see each other outside of Albert Square."
Brooks, who has played Janine since 1999, replied: "Don't like not seeing you every day!! Love you darling. Can't wait to see you VERY SOON."
Kellie Bright, who played Dyer's on-screen wife Linda, also paid tribute to the departing star, writing on Instagram: "My Mick…. It was only a matter of time… But who would have thought that it would have taken 9 years for Mick and Linda to finally come to an end. It has been, without a doubt, the best years of my life so far. For many reasons, but YOU @officialdannydyer are definitely one of them."
Dyer recently rejected rumours that he would be returning to the soap as Mick's body was never found.
Appearing on The Mo Gilligan Show, Dyer simply said: "I don’t want to come back."
He also compared his situation to Leslie Grantham's who famously returned as Dirty Den in 2003 after leaving the soap in 1989 after apparently being killed: "He [Grantham] was skint, he needed to come back. The geezer was on his arse. I don’t fancy it, Mo. I’ve done over 1000 episodes."
Watch below: Danny Dyer didn't want his daughter to enter Love Island.