But there is more to this than a simple coincidence, as 36 is a number with great significance in Judaism, the Jewish religion.
In a form of Jewish numerology known as gematria, the number 18 stands for “chai” in Hebrew, which means “life”.
Because 36 is twice 18, it is known to represent not one but “two lives” – and is commonly referred to as “double chai”.
Although Diana passed away over two decades ago, she still lives on in the memories of many around the world, with Elton John singing the lyric: “Your candle’s burned out long before your legend ever will,” at her funeral.
In Judaism, the number 36 has always held a special significance, because the light created by God on the day of creation is said to have shone for 36 hours.
Another significance is that the Torah, which is the Jewish holy book, also contains 36 commandments to love, respect and protect strangers.
According to the Talmud, the number 36 is “intriguing” for its mystical significance.
“It is said that at all times there are 36 special people in the world, and that were it not for them, all of them, if even one of them was missing, the world would come to an end.
“The two Hebrew letters for 36 are the lamed, which is 30, and the vav, which is 6.
“Therefore, these 36 are referred to as the Lamed-Vav Tzadikim,” said Rabbi Raymond A Zwerin in 2002.
“This widely-held belief, this most unusual Jewish concept is based on a Talmudic statement to the effect that in every generation 36 righteous “greet the Shekhinah”, the Divine Presence.”
The age 36 may be the age Diana died, but it is also a significant time for both Meghan and Kate, although for positive reasons.
Kate is due to give birth to her third child with Diana’s son Prince William, 35, while she is still 36, with a due date in April.
Meanwhile, Meghan will marry Prince Harry, 33, on May 19 2018 while she is also still 36.
Prince Harry took Meghan to visit his mother Diana’s grave after they got engaged, and will visit again ahead of their wedding.
“Harry wanted to take Meghan to see and speak to her (Diana), it was very personal for Harry,” a source told the Daily Star.
“I think he quietly asked his mum for her blessing to marry Meghan, too.”