Need clarification on 3 Conditions for Mortal Sin

I understand that there are 3 conditions for mortal sin.

1st condition - grave matter
2nd condition - sufficient knowledge

To fulfill the second condition, is it enough to know that the act is sinful, or do you have to know and understand the gravity of the act.

An example would be where someone is aware that it is a sin to miss mass, but is unaware of the gravity of the sin. i.e. that it is a mortal sin.

In this case, would it be a mortal sin?

Thanks

Catechism (underline added):

**1857 **For a sin to be mortal, three conditions must together be met: “Mortal sin is sin whose object is grave matter and which is also committed with full knowledge and deliberate consent.”

Someone needs to be aware of the gravity of the act to be fully culpable for it, otherwise it can’t be said that they truly have full knowledge of the sin.

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