Robert F. Kennedy Jr. did eat the McDonald's meal that he was pictured with on Trump Force One over the weekend, Donald Trump Jr. has confirmed.

Kennedy, who is Donald Trump's pick for health secretary, has promised to 'make America healthy again' and has long rallied against processed foods.

He has publicly criticized the President-elect's love of fast food, including McDonald's, describing the food he eats as 'poison' and 'really bad'.

But when Trump, Don Jr. and  Tesla CEO Elon Musk indulged in a 3am McDonald's run after the Ultimate Fighting Championship in New York on Saturday night, RFK Jr. also partook in the meal.

'We got back on the plane...Bobby did have, have some McDonald's. We definitely had some fun with that one,' the President-elect's eldest son told the Charlie Kirk podcast on Monday, adding that Kennedy 'definitely looks like he got his hand caught in the cookie jar with that one'.

Don Jr., admitting the photo he shared of the meal was his 'most viral Instagram post probably ever', said the four men were 'just having fun' after having pulled an 'all-nighter' - which he alleged was his father's third in two weeks.

'We joked, 'MAHA (Make America Healthy Again) starts on Monday.' Like all good diets, you've got to have a cheat day once in a while,' he added, noting that he has enjoyed the memes that stemmed from the photo.

House Speaker Mike Johnson was also asked about the photo on Monday. In video shared by CNN's Haley Talbot he told reporters: 'I think [Kennedy] did actually eat some of the McDonalds, I am not sure if I should say that, but I think he did.'

Kennedy, 70, flew with Trump aboard his plane to the UFC bout in New York on Saturday along with Musk and Don Jr.

The four men were shown seated in front of trays of McDonald's food in a photo posted online by Don Jr. on Sunday which he jokingly captioned: 'Make America Healthy Again starts TOMORROW.'