EXCLUSIVE

Naya Rivera's marriage to actor Ryan Dorsey came out of nowhere for everyone, except Naya -- who actually co-opted a lot of the ceremony from her planned wedding to Big Sean ... including the date.

Rivera and Dorsey tied the knot in Cabo San Lucas over the weekend. The longtime friends began dating right after Rivera broke off her engagement to rapper Big Sean in April.

According to our sources, the wedding date -- July 19 -- was the exact same date Naya and Sean were supposed to tie the knot. We're told Naya picked the date back in October when she and Sean got engaged.

The similarities don't end there ... according to reports, Rivera was married in a Monique Lhuillier gown -- which our sources say is the same designer of the dress Sean bought for Rivera for their wedding.

One more thing -- Rivera never gave back Sean's engagement ring, according to our sources. However, we don't know if she found a way to re-purpose that.

Mazel?

Ryan Dorsey's dad, Arnold, tells TMZ ... the date of the wedding might have been the same as the Rivera/Big Sean wedding ... but it also happens to be Dorsey's birthday.

Arnold says he found out about the wedding six weeks ago and while he was initially surprised, he said, "We didn’t question him. We are very happy for him. We trusted them and want what they wanted."