Prince William warned Prince Harry not to propose ...

Prince Harry claims Prince William warned him not to propose to Meghan Markle out of fear the couple’s relationship was moving “too fast.”

In his bombshell new memoir, “Spare,” he explained that William shot down the idea that Harry and Markle would “become a foursome” with him and Kate because she was “an American actress after all.”

Yet as the Duke and Duchess of Sussex got more serious, Harry told William he felt like their late mother, Diana, helped him “find” the “Suits” actress — which didn’t sit right with the Prince of Wales.

After making the bold claim, a “concerned” William “took a step back” and told his younger brother he was “taking things a bit too far.”

Prince William thought Prince Harry and Meghan Markle’s relationship was moving “too fast.”

Prince William thought Prince Harry and Meghan Markle’s relationship was moving “too fast.”

Despite William’s hesitancy, the couple got engaged in 2017 — a little over a year into their relationship.

However, the wedding planning process only drove a wedge further between the brothers.

The Prince of Wales had a lot of input when it came to the Sussex’s nuptials.

When it came to choosing a venue, William shot down the idea of Harry and Markle getting married at Westminster Abbey, where he and Middleton had tied the knot seven years prior.

He also didn’t want the pair to choose St. Pauls — where Princess Diana and King Charles wed in 1981 — because it was apparently “too grand” for their nuptials.

William didn’t like that Harry claimed their late mother helped him “find” his now wife.

While the wedding caused tension between the brothers, Middleton and Markle’s relationship also took a turn for the worse around the same time.

The two women got into a now-infamous fight over the bridesmaid dresses for the Sussexes’ big day — specifically regarding Princess Charlotte’s gown.

William said the two couples wouldn’t be “a foursome.”

According to Harry, the Princess of Wales texted Markle just days before their wedding about a “problem” with the fit of her daughter’s frock.

Middleton told the actress that Charlotte, now 7, “burst into tears” when she tried on the dress because it was “too big, long and baggy” and it needed to be completely redone.

Harry and Markle have been feuding with William and Middleton for years now.

After Middleton finally agreed to bring the youngster to the palace to get alterations, the two women got into a heated argument which left Markle in tears “on the floor.”

Although they were able to make amends the following day, the same can’t be said for the Fab Four’s relationship after “Spare” hits the shelves on Jan. 10.