The pair have amassed many fans ever since they announced they were a couple, who often gush about the loved-up duo when they post pictures together on social media.
In one of his most recent posts, the dad-of-three decided to share a video of him working out with girlfriend Kate, in what looks like a home gym.
Captioning the short clip, he wrote: '5am workout this morning... @meldeane12 getting us through it!!!! 💪🏽🤣'
But the seemingly innocent post didn't go down well with fans, who were quick to point out that it's not that bright outside at 5am in the UK, as sunrise is around 8am in January.
One wrote: 'Just putting it out there, it's not that light at 5am!', while another added: 'Very light outside for 5am?'
A third commented: 'I left work for work at 8.15am and it was still dark! 🤔'; and a fourth said: '@rioferdy5 looks pretty light for 5am, pretty sure the sun didn’t rise for a few hours later 😂'
Some fans suggested that the couple might not be in the country - as they spent New Year's in Dubai - which would explain why it's bright outside so early in the morning, but one disagreed: 'no that's his house, and Rio was in UK for the cup draw on Monday. It's a joke...he's playing with all these people and they fell for it!! 🤣🤣🤣 1-0 Mr F!'
Another fan also commented to say they thought it was a joke: 'Oh my god anyone else going to point out the 5am brightness!! It's called a joke 😳'.
Other fans decided to ignore the apparent blunder and just commented to say how cute the couple are for working out together.
One said: 'Got to love this! Couple goals nice to see Rio happy. He deserves it !!'
Another wrote: 'I love that you guys consistently work out together 💕 blood, sweat and tears is the fabric of family'