Learn Spanish (Latin America): Jamás voy a olvidar ese día.

When a negative word like jamás (never), nunca (never), or nadie (nobody) comes before the verb, you drop the no. You only need no if the negative word comes after the verb. Both Jamás voy a olvidar and No voy a olvidar jamás are perfectly correct, but you cannot say No jamás voy a olvidar.

Can I use nunca instead of jamás here? What's the difference?

Yes, you can say Nunca voy a olvidar ese día. Both words mean "never" and follow the exact same grammar rules. Jamás is just slightly stronger and more emphatic, adding a dramatic tone similar to "never in my life."

Why is it ese día and not esa día if the word ends in "a"?

Día is one of the most common rule-breakers in Spanish. Despite ending in "-a", it is a masculine noun (el día). Because it is masculine, it must be paired with the masculine demonstrative adjective for "that", which is ese.

Could I use the future tense olvidaré instead of voy a olvidar?