Adrianne Haslet FINISHES BOSTON MARATHON ... 3 Years After Losing Leg In Bombing

5:21 PM PT -- Adrianne just got a shout out from President Obama ... who wrote:

"Thank you, Adrianne, for being Boston Strong. Terror and bombs can't beat us. We carry on. We finish the race!"

SHE DID IT!!!

Adrianne Haslet has just crossed the finish line in the Boston Marathon ... 3 years after losing her leg while a spectator at the very same race.

Haslet -- flanked by friends and family members -- was emotional as she completed the race ... while a crowd of enthusiastic supporters cheered her on.

Haslet -- who had a "pit crew" to service her prosthetic leg along the course -- finished in just under 10 hours. But Adrianne had always made it very clear, it was never about time ... it was all about finishing the race for those who were unable to do so.

Earlier in the day, Haslet got mad props from Tom Brady ... well deserved props.

Congrats!!!