Sex and the City star Sarah Jessica Parker may have once played a witch in a movie but she didn't know her ancestor was accused of being one.
Actor Rob Lowe wanted to learn about his forebears' patriotism, but found out they fought against his country's founders.
And then there was the awkward moment when Brad Pitt and Angelina Jolie - like Kevin Bacon and his wife Kyra Sedgwick - found out they were cousins, although distant ones.
As celebrity genealogist Joshua Taylor has often discovered, sometimes family secrets are better left buried.
But for the most part, tracing your ancestry can be an eye-opening and exciting exercise.
The US expert, known for his starring role on the US version of the television show Who Do You Think You Are?, will help Kiwis get in touch with their own roots at the New Zealand Family History Fair, being held in Manukau this weekend.
His work with the show and the website www.findmypast.com has seen him delving into the family histories of many stars, often with unexpected results.
When it was discovered that Sarah Jessica Parker had a relative who was brought to trial for witchcraft at Salem in 1692, the actress was astonished.
"Here was something she'd read about in history books her entire life and that she had a family member directly involved in. She was obviously quite moved by the experience," Mr Taylor said.
So much so that she named her twin daughters Marion Loretta Elwell and Tabitha Hodge after ancestors who had been traced.
Rob Lowe found out his ancestor was a soldier on the wrong side of the American War of Independence, while Ashley Judd was flattered to learn her family members were on board the Mayflower when it arrived in the New World, Mr Taylor said.
"There have been a few instances when you come across something and you realise it's not suitable for TV. But you have someone in front of you who really wants to know, and they ask the question and you have to answer it."
Mr Taylor was introduced to the field by his grandmother, an avid genealogist who would take him through cemeteries and courtyards across the US. By the time he was 15, clients were paying him to look into their own histories.
So how far back could records usually take him?
"It really depends on where your family is from. Most people with UK roots can go back to 1750 or 1700 with some work."
A royal connection saw him trace one client's history back to 6AD.
The internet has revolutionised his work, but he believes graveyards and dusty library basements will still continue to have a place in it.
At a time when a growing number of young Kiwis are keen to explore their own family trees, he said it was important to know just how small the world becomes, the further you go back in time.
Where: Vodafone Events Centre, Manukau, today and tomorrow.