The "Jenny from the Block" singer and the retired baseball star got engaged after two years of dating during a vacation in the Bahamas earlier this month, and they have received an outpouring of well wishes and congratulations from friends, family and celebrity pals.
Alex revealed on Thursday night (March 21) that they also received an extra special congratulatory message - a handwritten note from Obama written on a small letterheaded card.
"Michelle and I just wanted to congratulate you on your engagement," the note reads. "After 26 years together, we can say that whatever challenges life may bring, sharing them with someone you love makes it all better."
He signed off by writing "all the best" along with his cursive signature.
The former sportsman shared a picture of the note on his Instagram page with the caption, "This means the world to us. #44."
Earlier this week, they spoke about being engaged for the first time, with Jennifer telling People: "We're really happy. We're constantly supporting each other in our individual endeavours and thinking about all the things that we can build together. Everything that we do, we do together. He knows my dreams and I know his dreams, and together we feel like we're stronger."
Alex added: "We have (an) appreciation for where we are in our lives today, and that's what we're enjoying the most."
The singer, who was presented with a 16-carat diamond ring during the proposal, has been married three times before, and shares 11-year-old twins Max and Emme from her marriage to third husband Marc Anthony, while Alex is father to two girls - Natasha and Ella - with his ex-wife Cynthia.