"Happy belated birthday to this beautiful soul!!!" Spears wrote in the photo caption to her little sister, who celebrated her birthday on April 4. "I love you so much and damn it I wish I was as smart as you at 30 !!!! It's weird to say that I was basically your momma when you were younger and yes I'm still older but your soul is and always has been wise !!!!"
She continued: "I’m truly and genuinely inspired by your path and the life you have created for your beautiful children and I'm so f---ing proud to call someone as beautiful inside as you my sister !!!!"
"And not only are you a beautiful soul you're so DAMN STRONG ... I was extremely taken back and still am to this very day !!!" she said, recalling a moment the sisters shared. "We play wrestled at home (such classy Southern chicks) and you put me to the floor in literally two seconds after I gave all my might ... I’ll never forget it !!! Maybe we should have a rematch ... I mean things have changed since 6 years ago !!!!! PS I wish I was as strong as you and happy birthday !!!!"
Jamie Lynn responded with a collection of cute emojis, while most of the other comments left on the post focused on Timberlake's unexpected appearance on Spears' Instagram feed.
In February, Timberlake reached out to Spears via a public apology on social media after the documentary Framing Britney Spears reported how he had portrayed her following their much-publicized split in 2002, when he made jokes about their sex life in interviews and cast a Britney look-alike in his damning "Cry Me a River" music video.
"I am deeply sorry for the times in my life where my actions contributed to the problem, where I spoke out of turn, or did not speak up for what was right," he wrote in a note on Feb. 12. "I understand that I fell short in these moments and in many others and benefited from a system that condones misogyny and racism. I specifically want to apologize to Britney Spears and Janet Jackson both individually because I care for and respect these women and I know I failed."
See the birthday post on Spears' Instagram account here.