Sandra Lee and Ben Youcef are officially done ... 'cause TMZ has learned the longtime couple has called off their engagement.

Sandra's rep, Jen Abel, confirms to TMZ ... the former Food Network star has ended the engagement after five years together.

The confirmation comes on the heels of our recent run-in with Sandra in NYC last week, and when we asked about wedding plans, she swerved hard ... pivoting to work instead of offering any kind of timeline.

Then came the moment that really raised eyebrows ... she wasn't wearing her engagement ring.

When we asked about it, Sandra brushed it off, saying her outfit didn't call for jewelry, but there was nothing on that finger, and the explanation didn't quite add up.

Sandra and the actor met in early 2021 and got engaged later that same year, making this a pretty established relationship.

As you know ... before Ben, Sandra was in a long-term relationship with former New York Governor Andrew Cuomo ... they split back in 2019 after 14 years together.