Simon, played by Nick Berry, makes a one-off appearance following the funeral of his mum Pat Evans, The Sun has revealed.
The special scene, which was only recorded yesterday, will see Simon pay a secret visit to Pat's grave in the dead of night to lay some flowers.
Simon does not attend the actual service as he has been arguing with his half-brother David (Michael French), who returned to Albert Square on New Year's Day to see Pat before she died.
EastEnders bosses are expected to air Simon's scene at the very end of tonight's episode after the credits have rolled.
The news comes after show chiefs promised an "extra special treat" paying tribute to Pat this evening.
Berry played the role of Simon between 1985 and 1990.
EastEnders airs tonight at 8pm on BBC One.
> EastEnders: Pat Evans's funeral in pictures
> Read our full spoiler for tonight's episode of EastEnders
> Read more EastEnders spoilers and news
Watch some of Pat's EastEnders best bits below: