Having defeated Riddle at WrestleMania 37 to claim the title last month, Sheamus is enjoying his third reign as the WWE United States Champion on RAW.

The 'Celtic Warrior' is currently on a mission to bring prestige back to the belt, hosting a regular "US Title Open Challenge" on Monday nights.

If that sounds familiar, it is because John Cena did exactly the same thing back in 2015.

Cena, now 44 years old, is a firmly established actor in Hollywood these days, having worked on a number of successful movies in recent years. In fact, his last last appearance in a WWE ring came last year at WrestleMania 36, where he faced 'The Fiend' Bray Wyatt in a Firefly Funhouse match (which turned out to be more of a cinematic angle than an actual bout).

Sheamus' ongoing storyline, though, has repeatedly seen Cena's name mentioned on television, with comparisons made between the United States Championship reigns of both men.

Now, Sheamus has stirred the pot even further.

The Irish Superstar took to social media on Saturday evening to share a picture of himself and Cena posing together during a training session.

"Here’s a picture of the GREATEST United States Champion and John Cena," declared Sheamus, with the caption clearly designed to take a friendly swipe at Cena.

The two Superstars - who each look in phenomenal shape in the photo - have always had a keen rivalry in the ring.

When Sheamus burst onto the scene in WWE in 2009, he dethroned Cena for the WWE Championship at that year's TLC pay-per-view event. The duo have also had a number of other matches against one another down the years, most recently on an episode of RAW in September 2015.

That bout, though, might not be the last time Sheamus and Cena square off.

John Cena Hinting at WWE Return

Recently, Cena teased a return to WWE with a pair of social media posts of his own. Should Cena make his way to RAW, Sheamus would seem to be his most logical target.

For the record, despite Sheamus' trolling this weekend, Cena has five United States Championships to his credit - compared to the Irishman's trio of reigns.

It will be interesting to see whether this recent social media activity leads to anything physical on WWE television in the coming months.