I recently discovered, via Spotify, a recording of a Duke Ellington performance which has not been made available before. 
My best guess is that the recording is taken from Duke Ellington's appearance at XIV FESTIVAL INTERNAZIONALE DEL JAZZ which took place in Bolgogna, Italy in 1973 whilst Ellington was on his final European tour.
The festival continues, annually, to this day and the website  says: 
 Nei giorni 8-9-10 novembre 1973 si tenne il XIV Festival Internazionale del Jazz che presentò interessanti gruppi di giovani: uno
italiano, la Big Band degli allievi del Conservatorio di Bologna diretta da
Ettore Ballotta, l’altro americano, “The Young Giants of Jazz” con Jimmy Owens,
Gary Burton, Cedar Walton e Roy Haynes. Furono inoltre presentati alcuni dei
miti che negli ultimi cinquant’anni avevano fatto grande e reso popolare il
jazz: la celebre orchestra di Duke Ellington, B.B. King, Sarah Vaughan, e, infine, Miles Davis.
Nei giorni 8-9-10 novembre 1973 si tenne il XIV Festival Internazionale del Jazz che presentò interessanti gruppi di giovani: uno
italiano, la Big Band degli allievi del Conservatorio di Bologna diretta da
Ettore Ballotta, l’altro americano, “The Young Giants of Jazz” con Jimmy Owens,
Gary Burton, Cedar Walton e Roy Haynes. Furono inoltre presentati alcuni dei
miti che negli ultimi cinquant’anni avevano fatto grande e reso popolare il
jazz: la celebre orchestra di Duke Ellington, B.B. King, Sarah Vaughan, e, infine, Miles Davis. 
Google translates this - very loosely - as:
'In the days 8-9-10 November 1973 was held the XIV International
Festival of Jazz which showed interesting groups of young people: one Italian,
the Big Band of the students of the Conservatory of Bologna, directed by Ettore
Ballotta, the other American, "The Young Giants of Jazz "with Jimmy
Owens, Gary Burton, Cedar Walton and Roy Haynes. They were also presented some
of the myths that over the past fifty years had made great and popularized the
jazz orchestra of the famous Duke Ellington, BB King, Sarah Vaughan, and finally,
Miles Davis.'
From the ever-reliable Ellingtonia discography, full details of the engagement are as follows: 
DUKE ELLINGTON AND HIS ORCHESTRA  Bologna, I       8
November 1973
Concert, Palasport
Mercer Ellington(t); Harold
"Money" Johnson(t,v); Barry Lee Hall, Johnny Coles(t,flh); Vincente
Prudente, Art Baron(tb); Chuck Connors(btb); Russell 
Procope(cl,as); Harold Minerve(cl,as,fl,pic);
Harold Ashby(ts,cl); Paul Gonsalves, Percy Marion(ts); Harry
Carney(cl,bcl,as,bar); Duke Ellington(p); Joe Benjamin(sb); Quentin White(d);
Anita Moore, Tony Watkins(v)
¬ Kinda Dukish                                    
_| Rockin' In Rhythm 
Creole Love Call         
Satin Doll        
Spacemen      
In A Sentimental Mood         
¬ Caravan      
_| In Triplicate (In Duplicate)          
New York, New York - vAMo            
I Got It Bad - vAMo    
Blem - vAMo  
Chinoiserie     
Basin Street Blues - vMJ       
Hello, Dolly! - vMJ      
Medley           
1. Don't Get Around Much Anymore           
2. Mood Indigo          
3. I'm Beginning To See The Light  
4. Sophisticated Lady            
Love You Madly - vTW         
Do Nothin' Till You Hear From Me - vTW   
One More Time For The People - vAMo,TW           
Things Ain't What They Used To Be    
Courtesy of Spotify, here is the album, with half an hour's worth of selections from the concert programme, recorded - and released - by RAI Radio in Italy.