Caitlyn Jenner's grandchildren call her ''Boom Boom''.

The 70-year-old reality star - who was formerly known as Bruce Jenner before undergoing gender reassignment surgery - has a whopping 19 grandchildren, and has said that to avoid confusion when it comes to gendered titles, the youngsters have taken to calling her ''Boom Boom''.

Speaking on British reality show 'I'm A Celebrity... Get Me Out of Here!' on Thursday (21.11.19), her campmate Kate Garraway asked her how many grandchildren she has, to which she responded: ''20 in December.''

And when asked what they call her, she added: ''They've come up with 'Boom Boom'. It kinda stuck, it was easy for them to say.''

But the former Olympian - who has six children of her own, and helped to raise Kris Jenner's four children during their marriage from 1991 to 2015 - doesn't mind her kids still calling her ''dad'', because she says she'll ''always'' be their father despite her transition.

She explained: ''My kids all call me dad, Kendall asked me first and I said 'dad', I'm your dad and I'll always be your dad till the day I die. But what they're really good at which shocks me all the time is when they're talking about me, 'My dad she...' and it's tough to change the pronoun in the middle of it.

''Bruce raised them and Caitlyn is enjoying their life with them.''

Caitlyn has Burt, 41, and Cassandra, 38, with first wife Chrystie Jenner, sons Brandon, also 38, and Brody, 36, with second wife Linda Thompson, and daughters Kendall, 23, and Kylie, 22, with Kris.

Meanwhile, the star recently said she felt people ''hated [her] guts'' when she came out as transgender in 2015.

She said: ''I trained 12 years for the games. I trained 65 years to transition in 2015. It was harder to do, it was less accepted.

'''Everyone loved the games, a lot of people when they see you transition hate your guts. Look at the quotes on Instagram. By far that was a lot more difficult.''

But the 'I Am Cait' star is proud of her accomplishments.

She quipped: ''I have the great double. Olympic decathlon champion and Glamour's Woman of the Year.''