The 68-year-old "Rocket Man" singer tied the knot with his partner at their estate in Windsor in south east England last December, on the ninth anniversary of their civil partnership, and on October 25, John posted a birthday message for him, reported Female First.
John, who has sons Zachary and Elijah, with David, wrote, "Happy Birthday to my beautiful, wonderful man. I will love you forever @davidfurnish. #ShareTheLove #HappyBirthday (sic)."
The couple, who met in 1993, have championed for same-sex couples to be allowed to marry in the UK for many years, with legislation allowing it coming into force in March 2014.
Last year's ceremony took place next to a Damien Hirst altar, and featured their two sons as the ring bearers, with the gold bands attached to cuddly rabbit toys which they carried up the aisle.