Black wore the jumper with distinction in 322 games for the Lions, the most matches played in club history.
The 2002 Brownlow medallist, who now works as the club's midfield coach, had his jumper 'retired' for 12 months.
"I think he was disappointed that they were scratching his name off the locker and putting mine on," Watts, pick No. 65 in the 2014 NAB AFL Draft, jokingly told the Lions' club website.
Fellow draftees Jaden McGrath (pick No. 73) and Josh McGuinness (pick No. 81) have been handed numbers 29 and 43 respectively.
Rookies Cian Hanley (No. 37), Matthew Hammelman (No. 40), Billy Evans (No. 46), and Hugh Beasley (No. 48) were also allocated their jumper numbers.
Jonathan Brown's famous No. 16 will be retired for the 2015 season – much like Black's No. 20 was this year.
New Lions numbers
#3 – ALLEN CHRISTENSEN
Most recently worn by: Brent Moloney
Most games (club history): Michael Voss – 283
#5 – MITCH ROBINSON
Most recently worn by: Jack Crisp
Most games (club history): John Murphy – 214
#9 – DAYNE BEAMS
Most recently worn by: Ash McGrath
Most games (club history): Ash McGrath – 214
#19 – JOSH CLAYTON
Most recently worn by: Jordan Lisle
Most games (club history): David McMahon – 218
#20 – JOSH WATTS
Most recently worn by: Simon Black
Most games (club history): Simon Black – 322
#24 – LIAM DAWSON
Most recently worn by: Joel Patfull
Most games (club history): Joel Patfull – 182
#29 – JADEN McGRATH
Most recently worn by: Andrew Raines
Most games (club history): Garry Wilson – 268
#31 – HARRIS ANDREWS
Most recently worn by: James Polkinghorne
Most games (club history): Bert Clay – 157
#37 – CIAN HANLEY
Most recently worn by: Patrick Wearden
Most games (club history): Keith Bromage – 41
#40 – MATT HAMMELMANN
Most recently worn by: Isaac Conway
Most games (club history): Scott Clayton – 160
#43 – JOSH McGUINNESS
Most recently worn by: Nick Hayes
Most games (club history): Beau McDonald – 91
#46 – BILLY EVANS
Most recently worn by: Sam Michael
Most games (club history): Colm Begley – 29
#48 – HUGH BEASLEY
Most recently worn by: Stephen Wrigley
Most games (club history): Ken Hinkley – 10
