Jessica Simpson ''freaked out'' before turning 40.

The 'Dukes of Hazzard' actress celebrated her milestone birthday last month, and marked the occasion by posting a picture of herself on social media, in which she donned a pair of jeans she hadn't worn for 14 years.

And now, the singer and actress has said she was stressed about turning 40, because it took her a while to ''accept'' her age.

Speaking about her birthday selfie, she said: ''Did I turn 40? That was a really random thing, because I haven't put jeans on through the whole time, I've been in sweats. I am like embracing the quarantine life. Yeah.

''I freaked out two months before I turned 40, not knowing that that age would even mean anything to me but then its like 41, 42 ... I've never calculated my age until now ... I'm accepting it slowly [laughs].''

Jessica put on the old jeans because she enjoys ''reminiscing'' about the past.

And the 'Blonde Ambition' star joked she's glad she put her memoir, 'Open Book', out earlier this year, because it would be ''800 pages'' long if she'd waited any longer.

During an appearance on SiriusXM's 'The Jess Cagle Show', she added: ''I just think I am such a person that reminisces, and I hold onto so many memories, I am tragically romantic like that about my own self ... wow 40, thank God I put a memoir out at 40, because it would have been 800 pages if I waited any longer.''

In Jessica's birthday snap, the star said she'd donned the True Religion denim in order to mark the ''final hours'' of her 30s.

She wrote along side the picture: ''I have kept these throwback True Religion jeans in my closet for 14 yrs (I'm not exaggerating!).

''I figured that since I'm in the final hours of my 30's I'd give them another try, and hello 40, so nice to meet you.''

And prior to her snap, she uploaded another image in which she posed on a beach in a bikini and hat as she prepared to say farewell to her 30s.

She accompanied the image with: ''YEE-HAW to my final days in my 30's. (sic)''