You need to incest three times rather than two to get 'A Perfect Circle' achievement.

[RhoxOS]

A Perfect Circle: Have only two distinct parents, grandparents, and great grandparents

This is the description of the achievement. To get only two distinct great grandparents, you only need to incest twice as your grandparents will share their mother and father.

O-O: Totaly foreigner Couple
　|
O-O: Sibling Couple
　 |
O-O: Sibling Couple
　 |
　 You
Like this.

However, achievement file asks for 'missing_unique_ancestors >= 50' for this achievement. If my assumption is correct, ck3 counts ancestors up to five levels. So if there is totally no inbreeding, there should be (2^6)-2 = 62 ancestors.

Each incest saves up [2^(6-i) -2] ancestors per stage. So, to save up to 50 ancestors, you need to incest three times, 30+14+6=50. Which would look like this.

O-O 　　　 　 O-O: Totaly foreigner couple's parents.
　 | 　　 　 　　 |
　 O------------O: Totaly foreigner Couple
　 　 　 |
　 　 　O-O: Sibling Couple
　 　 　 |
　 　 　O-O: Sibling Couple
　 　 　 |
　 　 　O-O: Sibling Couple
　 　 　 |
　 　 　 You

Which are 12 ancestors in total and that's 50 ancestors saved from a fully independent family tree.



TLDR: Achievement description is incorrect and you should incest three times

 

[pliznobn]

The things we do for love achievements.

 

[Leyrann]

So... this is based on the assumption that five generations are stored, and not four?

 

[RhoxOS]

So... this is based on the assumption that five generations are stored, and not four?

Yeah, and the achievement is actually achieved at three times rather than two. So some of the people are reporting this for bugs.

 

[VenetianPriest]

This is a very difficult achievement (I know its supposed to be). I'm now playing a fourth generation of inbreeding, i.e. sibling marriages. Great-great-grandparents, great-grandparents, grandparents, and parents are all sibling marriages. I'm married also to my sister, but it's 1441 and I doubt there is time left in the game to play a fifth generation. My sister and i are both inbred, so there's a great chance we won't have any children.

The challenging part I believe is the disputed heritage trait some heirs get well after birth. Because it's meant to be ambiguous, you never know for certain whether your purported father (in my cases it was always the mother alleged to have been unfaithful) is or is not your father.

So four generations of inbreeding and on paper it would appear I have met the conditions for this achievement.

As of this posting, no one has got this achievement.

 

[RhoxOS]

This is a very difficult achievement (I know its supposed to be). I'm now playing a fourth generation of inbreeding, i.e. sibling marriages. Great-great-grandparents, great-grandparents, grandparents, and parents are all sibling marriages. I'm married also to my sister, but it's 1441 and I doubt there is time left in the game to play a fifth generation. My sister and i are both inbred, so there's a great chance we won't have any children.

The challenging part I believe is the disputed heritage trait some heirs get well after birth. Because it's meant to be ambiguous, you never know for certain whether your purported father (in my cases it was always the mother alleged to have been unfaithful) is or is not your father.

So four generations of inbreeding and on paper it would appear I have met the conditions for this achievement.

As of this posting, no one has got this achievement.

I don't think the 'actual' father matters. In my community at least three of them got the achievement using Alfonso 6. If my memory is correct, I used the 'Here, let the grandpa help you a bit' method. Most players were confused about the condition itself.

 

[Vanhal]

Ah, a mathematics of incest. Useful to know.

 

[Alblaka]

I don't think the 'actual' father matters. In my community at least three of them got the achievement using Alfonso 6. If my memory is correct, I used the 'Here, let the grandpa help you a bit' method. Most players were confused about the condition itself.

Ah yeah, used that method too. Not for the achievement, mind you, but I had my grandson wed to the female ruler of the byzantine empire. Only then noticed he was swinging the other way. So I gave the Empress a quick tumble and we promptly had 'entirely legitimate' twins as heirs. They lasted a few years for being dethroned, regrettably.