Tom Brady turns 40 today -- and the fans in Boston let him know it with a screaming rendition of "Happy Birthday."

As Tom took the field at New England Patriots training camp Thursday morning, dozens of fans decked out in Pats gear -- some holding "Happy Birthday" signs -- belted out the song. 

Tom smiled and waved. 

The team also brought out a bunch of goats for the G.O.A.T. -- they're really blowing this thing out. 

His wife, Gisele, also posted a HBD message for him -- saying he makes 40 look like 20. She's right. 

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