Donald Trump Jr. fired off a nasty tweet Thursday, mocking Hillary Clinton on her 70th birthday for describing herself in her own year-old Twitter post as a “future president.”

“A year later the arrogance and entitlement in this tweet is exactly why it was never going to happen,” the president’s eldest son wrote.

“Happy Birthday to this future president,” the former first lady had tweeted last October.

Earlier, Trump Jr. took another shot, wishing Clinton “Happy Birthday Hillary” — with a birthday cake emoji — in a retweet of a Fox News post.

“FOX NEWS ALERT: DOJ lifts gag order, allows FBI informant to testify on Russian Uranium Deal in front of Congress,” read the Fox tweet, referring to the investigation into the sale of 20 percent of the US uranium supply to Russia during the Obama administration while Hillary was secretary of state.