Caitlyn Jenner welcomes sixth grandchild William Behr through her eldest son ...

On Sunday, transgender activist Caitlyn Jenner shared a sweet snap of herself posing with her sixth grandchild - newborn baby boy William Behr - who arrived on February 9.

Her eldest son Burt with ex-wife #1 Chrystie Crownover touchingly named the infant after his 69-year-old father-of-six, who was actually born William not Bruce.

The 40-year-old Gladiator Tires driver - who's always been supportive of the two-time Olympic gold medalist - also has a two-year-old son Bodhi with his girlfriend, Valerie Pitalo.  

Squeee! On Sunday, transgender activist Caitlyn Jenner shared a sweet snap of herself posing with her sixth grandchild - newborn baby boy William Behr - who arrived on February 9

Squeee! On Sunday, transgender activist Caitlyn Jenner shared a sweet snap of herself posing with her sixth grandchild - newborn baby boy William Behr - who arrived on February 9

Touching tribute: Her eldest son Burt with ex-wife #1 Chrystie Crownover named the infant after his 69-year-old father-of-six, who was actually born William not Bruce (pictured in 2017)

Touching tribute: Her eldest son Burt with ex-wife #1 Chrystie Crownover named the infant after his 69-year-old father-of-six, who was actually born William not Bruce (pictured in 2017)

'I'm very excited [about Caitlyn's gender affirmation]. Part of me was screaming to say, "Hey, I've known for 25 years and I've always been supportive!" I always will be,' Burt told Esquire in 2015.

'Before I was allowed to tell anybody, or before my dad even knew that I knew, I went and marched on behalf of Prop 8 through the streets of Los Angeles. I've always tried to be an outspoken supporter of the LGBT community.'

Jenner also has a one-year-old granddaughter Stormi (through Kylie), three-year-old granddaughter Eva (through Brandon), as well as a 10-year-old granddaughter Francesca & seven-year-old granddaughter Isabella (through Cassandra Marino).

The baby news came after the retired decathlete enjoyed Valentine's Day with her constant companion since 2017, Sophia Hutchins, inside her $3.5M, four-bedroom Malibu hilltop home.  

Caitlyn wrote: 'Welcome to the world William Behr Jenner. Congratulations @burtonjenner and @valeriepitalo !! Love you guys'

Caitlyn wrote: 'Welcome to the world William Behr Jenner. Congratulations @burtonjenner and @valeriepitalo !! Love you guys'

Big brother: The 40-year-old Gladiator Tires driver - who's always been supportive of the two-time Olympic gold medalist - also has a two-year-old son Bodhi (R) with his girlfriend, Valerie Pitalo (L)

Big brother: The 40-year-old Gladiator Tires driver - who's always been supportive of the two-time Olympic gold medalist - also has a

read more from dailymail.....

NEXT Abbie Chatfield shows off her toned figure in a skimpy pink houndstooth bikini ... trends now