After the couple’s engagement announcement in 1981, it seemed everything went downhill quickly.

Now, a royal author is sharing why she believes the king committed to Diana over the queen consort.

While Charles was married to Princess Diana, he was seeing Camilla behind the princess' back.

King Charles III posing for photo

So, why didn’t he pop the question to Camilla instead of Diana in the first place?

Royal author Angela Levin has a theory.

“King Charles had to have an heir and … “Because her whole aim is to keep the monarchy going.”

King Charles III and Princess Diana posing

Adding, “He was over 30, he had to find heirs.”