AWWWWWWWWWWWWW!!!
Tom Brady melted into a sweet bowl of love Monday ... writing a mushy birthday note to Gisele for her 40th -- and it's adorable as hell!!!
The G.O.A.T. fired up his social media account to deliver the message ... posting a pic of the supermodel and their kids, writing "Happy 40th Birthday" ... all while stealing some sappy lines from Frank Sinatra.
"You are the sunshine of my life," Brady wrote. "That's why I'll always be around. You are the apple of my eye. Forever you'll stay in my heart.