Former US President Donald Trump attacked Prince Harry on Sunday, accusing him of betraying his late grandmother Elizabeth II.

Trump criticized the way the current US President Joe Biden's administration handled the request of the Duke of Sussex, Prince Harry, who admitted to drug use, for a US residency visa.

Trump considered that the Biden administration provided protection to the prince in his battle to obtain the American visa, following his clear and explicit statements about his drug use.

Trump said in his interview with the "Sunday Express" newspaper: "Personally, I would not protect him; he betrayed the queen and that is unforgivable. I think Biden and his administration were very generous with him after what he did. If it were up to me, he would be alone without protection."

Prince Harry had admitted in his memoir titled Spare that he used drugs, smoked hashish, and took hallucinogenic drugs, including marijuana, cocaine, and magic mushrooms.

It is not clear whether Harry, who moved to California with his wife Meghan Markle in 2020, mentioned details of his drug use in the visa application.

John Pardo, a representative of the US Department of Homeland Security, told the court on Friday that "Harry's book was not a sworn testimony or evidence of drug use; just saying something in a book does not make it true."

He added: "People say things to sell books; Harry's immigration records should remain private."

The Heritage Foundation, a conservative research institute based in Washington, D.C., filed a lawsuit to force the Duke of Sussex to release his US immigration files.

Harry said last week that "US citizenship was just an idea that came to mind, but it is not a top priority for him right now."

Informed sources indicated that when applying for a US entry visa, foreigners are asked in the visa form of the Department of Homeland Security: "Have you ever been a drug user or addict," noting that Harry answered the request honestly.

Biden officials fought for several months the case filed by the Heritage company, arguing that all visa applicants have the right to privacy.