Seven-time major winner Palmer, who died at the age of 87 last September, was one of the stars of the game who wrote to Willett after his dramatic triumph at Augusta National.
The note has taken on extra significance this week as Willett prepares to play in the Arnold Palmer Invitational, the tournament Palmer started at Bay Hill in 1979 after buying the club four years earlier.
A 14-foot bronze statue of Palmer was unveiled at the course on Saturday, while Willett is among the players who will have the tournament's "umbrella" logo on his bag for the week.
"Having a green jacket at home for 12 months is pretty nice and you do get the letters come through afterwards," Willett said on a teleconference ahead of his Masters defence in April. "They really are pretty cool. They are the kind of things that you don't expect.
"Mr Palmer sent us a letter saying he had watched and how spectacular an event it was and then went into saying he hopes my wife and son Zach (born just before the Masters) are all well.
"Mr Palmer's been there and done it many times and I'm sure when he did it he had one of his idols potentially write him a note, but you never expect these things - you don't know what's going to happen when you win something like that.
"For people like Mr Palmer, who is such a legend of the game, who changed the game for all of us, for him to take the time to write you a letter really says something about the person that he was."
BETTING ODDS (via 888 Sport)
Leader after round one
- Rory McIlroy: 12/1
- Jason Day: 14/1
- Henrik Stenson: 14/1
- Hideki Matsuyama: 16/1
- Rickie Fowler: 25/1
- Justin Rose: 28/1
- Paul Casey: 50/1
Click here to place a bet.
Odds correct as of March 15 at 5pm.
- (USA unless stated, all times Local, -4hrs from BST):
- (x) denotes amateurs
Starting at hole 1
- 0735 | Kevin Na, Chez Reavie, Jason Kokrak
- 0747 | Martin Laird (Sco), Brian Harman, John Huh
- 0759 | Morgan Hoffmann, Trevor Immelman (Rsa), Cameron Smith (Aus)
- 0811 | Cody Gribble, Keegan Bradley, Charles Howell III
- 0823 | Billy Hurley III, Jim Herman, Ernie Els (Rsa)
- 0835 | Greg Chalmers (Aus), Charley Hoffman, Matt Every
- 0847 | Rod Pampling (Aus), Pat Perez, David Lingmerth (Swe)
- 0859 | Harold Varner III, Camilo Villegas (Col), Matthew Fitzpatrick (Eng)
- 0911 | Bud Cauley, Jamie Lovemark, Luke List
- 0923 | Kelly Kraft, Rob Oppenheim, Ryan Ruffels (Aus)
- 1220 | Seung-Yul Noh (Kor), Ian Poulter (Eng), John Daly
- 1232 | Kevin Chappell, Scott Brown, Patton Kizzire
- 1244 | Patrick Rodgers, Tim Herron, Jeunghun Wang (Kor)
- 1256 | Hideki Matsuyama (Jpn), Henrik Stenson (Swe), Justin Rose (Eng)
- 1308 | Jason Day (Aus), Bubba Watson, Martin Kaymer (Ger)
- 1320 | Tony Finau, Fabian Gomez (Arg), Stewart Cink
- 1332 | Kevin Kisner, Vaughn Taylor, Billy Horschel
- 1344 | Si Woo Kim (Kor), Mackenzie Hughes (Can), Sean O'Hair
- 1356 | Marc Leishman (Aus), Chad Campbell, Graham De Laet (Can)
- 1408 | Thorbjorn Olesen (Den), Brandon Hagy, Robby Shelton
Starting at hole 10
- 0735 | Lucas Glover, David Hearn (Can), Ollie Schniederjans
- 0747 | Greg Owen (Eng), Louis Oosthuizen (Rsa), Byeong-Hun An (Kor)
- 0759 | Kyle Reifers, Russell Henley, Wesley Bryan
- 0811 | Adam Hadwin (Can), Rickie Fowler, Graeme McDowell (Nirl)
- 0823 | Rory McIlroy (Nirl), Brandt Snedeker, Sam Saunders
- 0835 | Brian Stuard, Chris Kirk, Paul Casey (Eng)
- 0847 | Retief Goosen (Rsa), Aaron Baddeley (Aus), Alex Noren (Swe)
- 0859 | James Hahn, William McGirt, Branden Grace (Rsa)
- 0911 | Boo Weekley, Derek Fathauer, Thomas Pieters (Bel)
- 0923 | Grayson Murray, J.J. Spaun, Curtis Luck (Aus)
- 1220 | Geoff Ogilvy (Aus), Francesco Molinari (Ita), Anirban Lahiri (Ind)
- 1232 | Daniel Summerhays, Kyle Stanley, Tommy Fleetwood (Eng)
- 1244 | Harris English, Kevin Streelman, Cheng-Tsung Pan (Tpe)
- 1256 | Danny Willett (Eng), Charl Schwartzel (Rsa), Ben Martin
- 1308 | Ryan Moore, Hudson Swafford, Emiliano Grillo (Arg)
- 1320 | Vijay Singh (Fij), Smylie Kaufman, Tyrrell Hatton (Eng)
- 1332 | Danny Lee (Nzl), Steven Bowditch (Aus), Brooks Koepka
- 1344 | Troy Merritt, Zach Johnson, Webb Simpson
- 1356 | Steve Wheatcroft, Roberto Castro, Michael Kim
- 1408 | Robert Gamez, Matthias Schwab (Aut), David Hronek