Britney Spears Gushes Over Son Jayden as He Takes Her on a Drive

Britney Spears may be the Princess of Pop, but at heart, she’s just a mom -- and in a rare glimpse, she let fans in on a tender moment with her son Jayden.

In a rare IG cameo, Britney’s 18-year-old son Jayden looked cool and carefree behind the wheel -- while she played proud passenger, focusing the camera on him and even reaching over to lovingly sweep his hair out of his face.

Britney was totally floored in the caption -- gushing that Jayden’s now 6'3" with giant hands ... and she’ll never stop being in shock at how grown he is.

The singer called herself blessed, but couldn’t resist a cheeky warning in the caption, apparently telling Jayden to "please be careful with my heart."

Britney and Jayden seem to share a solid bond -- just a few months back in March, she proudly posted clips of him flexing his smooth piano skills.

As you know ... Jayden’s the younger brother of 19-year-old Sean Preston. Britney was largely estranged from both boys during their teen years while they lived with dad Kevin Federline.