Reese Witherspoon has posted a sweet tribute to her son Tennessee in celebration of his fifth birthday.

The 41-year-old star has her youngest son with her husband Jim Toth, and took to Instagram on Tuesday (26.09.17) to praise him for bringing her ''so much joy'' as he celebrates his special day.

Posting a photo of Tennessee holding a large balloon in the shape of the number five, Reese wrote: ''Happy Birthday to my littlest guy , Tennessee! Everyday you bring us so much joy with your sweet smile and beautiful laugh. I love you so much! #feeling5 #HBD (sic)''

The adorable post comes after the 'Big Little Lies' star made a similar tribute earlier this month in celebration of her daughter Ava's 18th birthday, in which she revealed she was ''amazed'' by her eldest child.

Reese - who has Ava with her ex-husband Ryan Phillippe, with whom she also has 13-year-old son Deacon - wrote at the time: ''Happy 18th Birthday to my sweet girl @avaphillippe ! Your kindness, grace, intelligence and humor never cease to amaze me. I love you and your HUGE [heart] and I feel so lucky that I get to be your mom. #proudmom #18 (sic)''

The 'Legally Blonde' actress is no stranger to gushing about her family either, as she previously admitted she puts her brood before her career, and often ''really needs to think'' about taking on each project and working out how it will fit around her home life.

She said: ''Every time a movie comes up, I balance my kids' wants and needs versus my own.

''My job takes me far away, I have to travel to different countries and I might not see them until the weekend when I'm exhausted, so when I take a movie, I really need to think about that.

''Right now, Ava is applying for college, so I don't work on acting jobs.

''There have been several movies I wanted to make and didn't because of my kids and I wish I had made them.''