Lacey Turner and Jessie Wallace were left wiping away tears during an emotional episode of EastEnders ' spin-off, Secrets From The Square, on Thursday night.
The EastEnders actresses sat down with Stacey Dooley before being asked to watch a scene from the past, which opened the flood barriers.
In the scene, Albert Square's favourite black cab driver, Charlie Slater, died in the arms of Kat Moon, leaving the character in hysterics as she screamed for her family to come.
While watching the scene, Lacey, who plays the role of Stacey Fowler, became emotional before tears started rolling down her face as the scene progressed.
Jessie, who portrays Kat Moon, also began crying.
The pair were overcome with emotion while watching Derek Martin's final scene - a man with whom they had an unbreakable bond and are still in contact today.
Derek's final moments on Albert Square sent shockwaves through the homes of viewers, following his dramatic feud with Kat.
The father and daughter duo eventually made peace, which was set to last just seconds.
Sadly, he went on to have a sudden heart attack and died shortly before paramedics could arrive.
Speaking about the emotional sequence, Lacey said: "It's so hard to watch."
Jessie went on to say Derek had been a father figure to both actresses while on the set of EastEnders.
Lacey added: "It's really hard to watch an older person act a death because obviously that's what you get scared about when you get old."
"Just a lovely, lovely man. Really funny, caring, and a great actor," Jessie told Stacey.
While speaking about their everlasting bond, Lacey gushed: "He looked at us like his girls, and he will still now phone us up."
EastEnders is set to make an explosive return to BBC One on September 7.