Leading up to this day, EJ had dropped several hints about a proposal coming soon. The first (and biggest) hint came when the jeweler called to check in with EJ while his phone was connected to their SUV while on a drive with Mark. While EJ eventually returned the call, Mark sent a text to Tanisha wondering, "why does EJ have a jeweler saved in his phone?" She said, "don't worry about it, and stop asking questions!" The day before the proposal, Mark had to work because EJ utilized his Wegmans connections to make sure Mark's boss switched Saturdays with him. This allowed EJ to get everything set for the big day.
That morning, EJ, and Mark met up with Austin, EJ's friend since high school, to take anniversary photos. Mark had it in his head that this was when the big moment would come since EJ suggested he dress nicely. Once the pictures were done, and they watched Austin drive off, EJ suggested they drive to Winthrop to go to where their story all started. During the ride, EJ asked Mark what was wrong to which he replied nothing (as he tried to figure out why EJ wasted a photo opportunity for the expected proposal - a requirement Mark had asked for in a proposal). EJ took Mark on a walk to the beach across from his old apartment with the Boston skyline in the background. There he told Mark that he had written letters to Mark's mom, Linda, and cousin Allie asking for their blessing (another proposal requirement of Mark's), but had one more note he had written. That letter was written to Mark's father, Joe, that he gave to Mark to read.
In it, EJ discussed how grateful he was to Joe and Linda, for having Mark, and how he wishes he had the opportunity to have met him. He promised Joe that he would be a good husband to Mark, and a good father to Joe's future grandkids. He ended the letter by thanking Joe for being witness to when he proposed to Mark. After the longest four and a half minutes of EJ's life, when Mark finally finished reading the letter through tears, EJ got on one knee, and asked Mark to marry him. Once they embraced, Austin popped out from her hiding space to assure Mark she captured the moment (fulfilling the final requirement of making it a surprise).
After a few quick phone calls, they returned home to an apartment full of close family, and friends, yet again surprising Mark, who had the gasp heard 'round the world. Mark then asked EJ if they could cancel their dinner reservations so they could celebrate with everyone to which EJ agreed, since the dinner reservation was simply a decoy to hide the surprise party. EJ knew Mark had suspicions about the proposal coming, but was thrilled he was able to pull off the surprise party without a hint of speculation from Mark.