Donald Trump, the former US president and a potential rival to President Joe Biden in next year's election, has strongly criticized Biden for not attending the coronation of Charles III, the UK's new king.

In an interview with British right-wing broadcaster GB News on May 4 (local time), Trump said, “Certainly, he should be here (in the UK) as our representative of our country,” adding, “I was very surprised, I think it’s very disrespectful for him not to be here.”

He continued that If he were president, he would have attended as he thinks it's a very important event.

The coronation of King Charles III is set to take place on May 6. Despite the UK being the US's closest ally, President Biden will not attend, instead sending First Lady Jill Biden and a US delegation. Earlier this month, Biden expressed his desire to meet with Charles III in person during a phone call with the new king.

Around 100 heads of state from 203 countries will attend the coronation, with the number of attendees estimated to be over 2,200, according to British media.

There has been criticism in some UK circles that it is a diplomatic faux pas for the leader of their closest ally, the United States, not to attend the ceremony.

However, there is precedent for this: in 1953, during the coronation of Queen Elizabeth II, then-US President Dwight Eisenhower also did not attend, sending a delegation instead.

President Biden did attend Queen Elizabeth II's funeral.

Trump also appeared to associate Biden's absence from the coronation with the latter's age, which is 80.

“I don’t think he can do it physically, actually, I think that it’s hard for him to do it physically,”  Trump said, adding, “He’s got a lot of things going, a lot of strange things happened.”

The implication is that President Biden's advanced age makes it difficult for him to undertake foreign trips. Trump himself is 76 this year.

The Republican Party often uses Biden's age as an attack point. Indeed, President Biden has been known to make frequent verbal gaffes during speeches.