Jane Fonda Gives Up Hilariously Truthful Secret to Long-Lasting Beauty

Jane Fonda's looking phenomenal months after announcing her cancer went into remission ... and she's giving us some hilarious advice on how to look as great as she still does.

We got the legendary actress Thursday in NYC as she was heading into "The Late Show with Stephen Colbert" ... she said she's doing okay, and tossed up a peace sign for fans and photogs.

We asked the obvious question, in light of how great she's looking ... "What's the secret?" Newcomers gotta see this, because JF kept it 💯!!!

She told us all ya need is, "Good genes and a lot of money."

Yeah, you can tell her spirits are up after revealing last September she had non-Hodgkin's Lymphoma. She underwent chemotherapy for 6 months, and then announced the cancer's in remission.

As she described the good news, at the time, "BEST BIRTHDAY PRESENT EVER!!!"