Troy Deeney's 97th-minute winner, 20 seconds after Manuel Almunia saved Anthony Knockaert's penalty, mirrored the events at Griffin Park a fortnight earlier.
Dean was in the Brentford side who were a last-minute spot-kick from securing promotion, only for Marcello Trotta to hit the crossbar and Doncaster to break clear and score at the other end to clinch the League One title.
The Bees' promotion bid is still alive, however, as they prepare for the play-off final against Yeovil on Sunday.
Defender Dean wrote on Twitter: "Unbelievable scenes at Watford yesterday. Never thought I would see anything like that ever again after the Doncaster game. Crazy year!"