WWE Universe captured the couple celebrating after the match:
After the match, Cena grabbed the mic and expressed his love for Nikki, and then he proposed:
WWE provided video of the sequence:
The rivalry between the two sides dates back several weeks to Elimination Chamber, as Nikki and Maryse had a run-in backstage while Bella was brawling with Natalya.
That carried over to SmackDown when Nikki and Nattie once again got in Maryse's way, resulting in the French-Canadian superstar hitting Nikki with a steel pipe.
Later that same night, The Miz was eliminated by Cena in a Battle Royal to determine the No. 1 contender for the WWE Championship, but Miz went back in the ring and tossed Cena out to deny him an opportunity to face Bray Wyatt.
From that point forward, Miz and Maryse made it a point to run down Cena and Nikki both as individuals and with regard to their relationship.
Perhaps the best example of that was an episode of Talking Smack during which Miz labeled Cena as a heartless, soulless egomaniac who was only worried about himself.
Also, according to WWE's official Twitter account, Maryse suggested that the Cena and Nikki had a fake relationship:
In addition to that, she rubbed it in Nikki's face that Cena had yet to propose to her and was seemingly steadfast in his refusal to get married:
Maryse further criticized Nikki's character the following week on SmackDown when she accused the Bella Twin of going behind her back to land a contract with WWE and to be part of the first season of Total Divas.
There were clearly deep-rooted issues between Maryse and Nikki, although the same can be said for The Miz and Cena dating back to their match at WrestleMania 27.
The A-Lister defeated Cena to retain the WWE Championship, but only after The Rock lent a helping hand. Miz then dropped the title to Cena just a few weeks later, which further contributed to his disdain toward the leader of the Cenation.
Miz has battled to get back to the top of WWE ever since that feud with Cena, and while he hasn't yet won his second world title, a tag team match against Cena at The Showcase of Immortals represented a huge opportunity to get back in the conversation.
Sunday's bout turned out to be a stage for WWE to celebrate Cena and Nikki, but Miz's involvement could still bode well for him moving forward.
He has recently done some of the best character, mic and in-ring work of his career, which means a potential WWE Championship run could be in his future despite the loss to Cena.
Listen to Ring Rust Radio for all of the hot wrestling topics. Catch the latest episode in the player above (warning: some language NSFW).