Duffen, who led Hull to promotion to the Barclays Premier League in 2008, departed the club following an acrimonious legal dispute with previous owner Russell Bartlett three years ago.
But the 54-year-old was back in the directors box for Hull's 4-2 defeat at Palace, sporting the Tigers' club tie, after being offered the hand of friendship by the current owners.
Duffen said: "After all that I endured after leaving Hull under the previous regime, this has real resonance for me.
"It is the new Hull owners, with whom I have a very good relationship, acknowledging that I did nothing wrong in my time at the club and welcoming me back into the fold. It's a wonderful gesture."
Duffen, who agreed a settlement ending his dispute with the club's previous regime in February 2010, is keen to get back into football and would not rule out a return to the KC Stadium.
- Sports & Recreation
- Barclays Premier League