Kensington Palace laid to rest speculations of "Will they, won't they" Monday, announcing that Princess Kate Middleton and Prince William were expecting their third child together.

The Duke and the Duchess of Cambridge are already parents to three-year-old Prince George and two-year-old Princess Charlotte.

“Their Royal Highnesses The Duke and Duchess of Cambridge are very pleased to announce that The Duchess of Cambridge is expecting their third child,” a statement said.

“The Queen and members of both families are delighted with the news,” it said.

Speculations over the third child were always there, and had gained ground during the couple's trip to Poland in July.

During their trip to Warsaw, Kate and William were given a gift for a newborn, a toy bear, which prompted the Duchess to jokingly say: "We will just have to have more babies!" according to a People magazine report at the time.

Julia Sielicka-Jastrzebska, whose firm was said to be the manufacturer of such toys, said that Kate made the comment after being made aware the toy bear had been designed to comfort new born babies by replicating the sound of the womb.

Julia said: "We gave the Duchess some presents for Prince George and Princess Charlotte. She said they should have more babies and they laughed."

However, this humorous aside triggered an open letter by a San-Francisco based children's organization called "Having Kids," requesting the royal couple not to have another child.

The company, which is known for promoting smaller families, had posted the open letter on their official website, "respectfully" asking William and Kate to "consider forgoing having a third child."

The letter, which was signed by the company's president Carter Dillard and executive director Anne Green, mentioned the amount of influence the Duke and the Duchess have as public figures, and thus the ability and power they have to "model a sustainable small family."

The letter also cited environmental reasons like economic equality, climate change and the distribution of resources for having a sustainable family.

It continued: "Of course, we know that Prince George and Princess Charlotte are certain to have wonderful lives, protected from the deprivations of poverty and the threat of environmental degradation. They will receive optimal amounts of care and attention, as well as the best possible education. But the same can't be said of every future child."

The letter concluded by describing the "Fair Start family planning model" and it read: "Rather than having a third or more children, families consider forgoing another child and taking part of the substantial resources saved to help a different family plan a fair start in life for their child. The point is simply this: Family planning should be child-centered, and the Fair Start model is a serious move towards ensuring all children get the equal opportunities in life they deserve. And that they do so in a healthy, safe, and greener environment."

The royals did not respond to the letter, however the organization received backlash from royal well-wishers as they claimed that the organization was no one to interfere into the royal matters, according to Hello magazine.

The announcement by the palace demonstrates the organization's plea fell on deaf ears.

During her first two pregnancies, Kate, 35, has been suffering from acute morning sickness, also known as Hyperemesis Gravidarum. According to the statement from the palace, Kate is also suffering from the same condition during this pregnancy as a result of which she cancelled her planned engagement at the Hornsey Road Children's Centre in London on Monday morning.

"As with her previous two pregnancies, The Duchess is suffering from Hyperemesis Gravidarum. Her Royal Highness will no longer carry out her planned engagement at the Hornsey Road Children’s Centre in London today," the statement said.

"The Duchess is being cared for at Kensington Palace."